Transcriptional and post-transcriptional regulation of the jasmonate signalling pathway in response to abiotic and harvesting stress in Hevea brasiliensis
© Pirrello et al.; licensee BioMed Central. 2014
Received: 15 April 2014
Accepted: 19 November 2014
Published: 2 December 2014
Latex harvesting in Hevea brasiliensis amounts to strong abiotic stress that can cause a halt in production in the most susceptible clones. Although the role of jasmonic acid has been suggested in laticifer differentiation, its role in latex production and in the response to harvesting stress has received very little attention. Only a few key genes acting in the COI-JAZ-MYC module have been isolated and studied at transcriptional level.
Use of a reference transcriptome obtained on rubber clone PB 260 covering a large number of tissues under different environmental conditions enabled us to identify 24 contigs implicated in the jasmonate signalling pathway in the rubber tree. An analysis of their expression profile by qPCR, combined with hierarchical clustering, suggested that the jasmonate signalling pathway is highly activated in laticifer cells and, more particularly, in the response to harvesting stress. By comparison with their genomic sequences, the existence of regulation by alternative splicing was discovered for JAZ transcripts in response to harvesting stress. Lastly, positive transcriptional regulation of the HbJAZ_1405 gene by MYC was demonstrated.
This study led to the identification of all actors of jasmonate signalling pathway and revealed a specific gene expression pattern in latex cells. In-depth analysis of this regulation showed alternative splicing that has been previously shown in Arabidopsis. Interestingly, genotypic variation was observed in Hevea clones with contrasting latex metabolism. This result suggests an involvement of jasmonate signalling pathway in latex production. The data suggest that specific variability of the JA pathway may have some major consequences for resistance to stress. The data support the hypothesis that a better understanding of transcriptional regulations of jasmonate pathway during harvesting stress, along with the use of genotypic diversity in response to such stress, can be used to improve resistance to stress and rubber production in Hevea.
Jasmonic acid (JA) is a key hormone in the development of plant responses to abiotic stress, such as wounding . This plant hormone also plays a key role in the biosynthesis of secondary metabolites . It is particularly involved in the response to oxidative stress since it activates the ascorbate-glutathion cycle for the reduction of these major antioxidants ,.
The jasmonate biosynthesis and signalling pathways have been very widely studied and described in Arabidopsis using the analysis of mutants . The jar1 mutant is deficient in certain responses to JA, including ascorbate production to prevent oxidative stress . The JAR1 enzyme catalyses the conjugation of jasmonate to isoleucine (JA-Ile) . JA-Ile is the bioactive form of JA . It was demonstrated recently that COI1 is the JA receptor and can interact directly with JA-Ile . For its part, the coi1 mutant also shows insensitivity to JA, thereby causing male sterility, resistance to the inhibition of root development by JA, and a defect in the expression of genes regulated by JA . COI1 is an F-box protein  forming, with some other partners, a complex of the E3 ubiquitin ligase type, SCFCOI1 ,. This type of complex is involved in the ubiquitination of target proteins, leading to their subsequent degradation by the 26S proteasome . JASMONATE ZIM DOMAIN (JAZ) proteins are recognized by the SCFCOI1 complex. JAZ degradation enables the release of transcription factors such as MYC2,3 and 4 . The latter bind to cis-acting elements of the G-box type  present in the promoters of JA response genes and they initiate their transcription -. In addition to the MYC transcription factors, JAZ are able to interact with other transcription factors of the MYB, EIN3, EIL, ERF, GAI, RGA and RGL1 types, suggesting that they play a role in the interaction of the JA signalling pathway with those of other hormones ,. In Arabidopsis, JAZ proteins comprise 12 members which are characterized by the presence in the C-terminal position of the highly conserved domains, Jas and ZIM (TIFY). The Jas domain enables interaction with COI1 and with transcription factors, while the TIFY domains involved in dimerization and in the interaction with NINJA -. At the moment, the most likely model concerning the repression of genes induced by JA is an interaction of JAZ with TOPLESS (TPL). This interaction may necessitate the presence of the NINJA protein as an adapter, unless the JAZ protein possesses an EAR domain (ERF-associated amphiphilic repressor) to which TPL binds . The transcriptional regulation of JAZ can occur via MYC2 , but other components might be involved. Indeed, in the myc2 mutant, most JAZ were expressed following infection with Pseudomonas syringae . The sub-unit of the mediator complex, MEDIATOR25 (MED25), was recently identified as an integrative node of JA-dependent gene expression . At post-transcriptional level, most JAZ genes can be regulated by alternative splicing. In Arabidopsis, it has been found that intron/exon organization in the region of the Jas domain is conserved in the majority of JAZ genes . In Arabidopsis, the spliced form of JAZ10 has a Jas domain that is partially (JAZ10.3) or totally truncated (JAZ10.4) . Ectopic expression of JAZ10.3 and JAZ10.4 affords dominant insensitivity to JA as a consequence of the stabilization of the JAZ protein ,. The physiological role of isoforms with a truncated Jas domain in attenuating hormonal response has been suggested by various studies ,. Many studies have shown the importance of alternative splicing in plant development, but also in the response to stress (for review ), though that link has never been demonstrated in the case of post-transcriptional regulation of JAZ genes.
Hevea brasiliensis is the only commercial source of natural rubber (NR). NR is synthesized in the rubber particles of latex cells. Those cells differentiate from the cambium then anastomose to form an articulated network: laticifers. Latex is harvested by tapping the tender bark (phloem tissues). After latex flow, rubber particles agglomerate and clog the tapping zone. Latex is regenerated within a few days. In order to stimulate latex production 2.5% ethephon (an ethylene releaser) is applied to the tapping panel. Tapping and stimulation frequency is usually adapted to the metabolic activity of Hevea clones. In extreme cases of environmental or man-made stress due to rubber tree tapping, an oxidative burst occurs in the laticifers. That oxidative stress leads to peroxidation of lipids in the membrane of lutoids (poly dispersed lysosomal vacuome), which contain agglutinins such as heveins. The release of these factors leads to the in situ coagulation of rubber particles: this is the physiological syndrome known as Tapping Panel Dryness (TPD) . TPD causes substantial NR production losses (10-40%) and economic models predict that NR production will not be sufficient by 2020. The genetic variability existing within the different cultivated rubber clones shows that the intrinsically most productive and fast growing clones are also the most susceptible to abiotic stress and TPD . Some rubber clones with a slow laticifer metabolism are more tolerant of TPD. To date, few selected clones have the latter characteristics . For instance, clone PB260 is a clone with an active metabolism that is highly susceptible to TPD, while INC53 and RRIM600 are clones with a slower metabolism and are more resistant to TPD. The physical wounding caused by tapping, the osmotic shock within the laticifers due to latex flow, and metabolic activation linked to latex regeneration between two tappings amount to harvesting stress which causes diverse responses, including the production of hormones such as JA. In fact, wounded tissues produce systemin, which induces JA production . Interestingly, jasmonate and wounding are also involved in laticifer differentiation . It was recently shown that jasmonate acts as a signal molecule in rubber biosynthesis . Although the jasmonate signalling pathway has been studied in the rubber tree in connection with rubber biosynthesis and laticifer differentiation, little is known about its role in the response to harvesting stress. To date, only the ethylene biosynthesis and signalling pathways have been largely studied in this connection, and notably the transcriptional regulation of ERFs (Ethylene Response Factor) -. In Hevea, one or two members of the multigene families encoding COI , JAZ  and MYC  have been identified. Studies on the expression profile of those genes suggest the importance of JA in latex production. Indeed, HbCOI1 is strongly expressed in laticifers , the transcripts of HbJAZ1 accumulate in response to tapping and wounding , and HbMYC1 and HbMYC2 are more abundant in latex. HbMYC1 is induced by regular tapping and wounding, while the expression of HbMYC2 is not altered by those stimuli .
In this study, the availability of Hevea transcriptomic and genomic resources made it possible to identify all the different genes acting in the jasmonate signalling pathway and characterize their implication during development, and in response to abiotic stress. Among the transcriptomes sequenced on different tissues (latex, bark, leaves and stem tips) -, a reference transcriptome covering a large number of tissues and environmental conditions has been published for rubber clone PB 260 . An analysis of the structure of JAZs genes based on the genomic sequences of rubber clone CATAS 7-33-97 (BIG-CATAS Project, unpublished data), and an analysis of the corresponding transcripts revealed the existence of a mechanism of alternative splicing of JAZ gene transcripts. Thus, this study suggested that the stress caused transcriptionally and post-transcriptionally by latex harvesting regulates the jasmonate signalling pathway in Hevea.
For the transcript analyses, plant material of clone PB 260 grew in accordance with the conditions described in Duan and coll. . Samples corresponding to reproductive tissues (immature and mature, male and female flowers, zygotic embryos) were added to this study. Flowers were collected from 15-year-old trees. Zygotic embryos were collected from 5-year-old trees. In vitro plantlets of clone PB 260 were obtained by somatic embryogenesis with line CI07060. The plantlets were acclimatized and grown for 3 months in a greenhouse at a temperature of 27°C with 45% humidity. Several treatments mimicking abiotic stress were carried out, such as wounding, methyl jasmonate (MeJA), ethylene (ET) and dehydration at 1, 4, 8 and 24 hours. Drought stress response was controlled by following HbERFIVa3 (orthologue to DREB2A) transcript accumulation during this stress , whereas efficiency of wounding, ethylene and MeJA treatment were controlled using HbERF-IXc4 and HbERF-IXc5 (orthologue to ERF1) ,. The bark was wounded every 0.5 cm by scarification with a razor blade. The ET and MeJA treatments were carried out by placing the plants in a 300-l open-door Plexiglas box overnight before treatment. Five parts per million of pure ET gas (1.5 ml/300 l) was injected into the sealed air-tight box. A concentration of 100 μl of liquid ≥95% MeJA solution (Sigma, St Louis, MO) was diluted in 500 μl of absolute ethanol and then placed on Whatmann paper inside the box for gas release. Control plants used for the ET and MeJA treatments were placed in the box and exposed to air only. The dehydration treatment was carried out by taking the plants out of their pots and leaving them to dry under laminar air flow. Each sample was collected 1 h, 4 h, 8 h and 24 h after treatment.
RNA samples were collected and prepared at the CRRC, RRIT, Sanam Chaikhet District, Chachoengsao 24160, Thailand (13.39°N latitude and 101.26°E longitude). These locations and our activities did not require any specific permission. The field studies did not involve endangered or protected species.
Total RNA extraction
Total RNAs were extracted from one gram of fresh matter using the caesium chloride (CsCl) cushion method adapted from Sambrook and coll. (Sambrook et al. ) by Duan and coll. (Duan et al. ). DNA contamination was checked by PCR amplification using primers of the actin gene.
Primer design and transcript abundance analysis by qPCR
Total RNA integrity was checked by electrophoresis. For each candidate gene a blast was performed against the transcriptome of PB 260, to define highly conserved regions. The qPCR primers were designed outside these regions using the Primer 3 module of Geneious Pro software version 5.3.6 (Biomatters Ltd., New Zealand). Each primer pair was blasted against the transcriptome library. qPCR and the fusion curve of the PCR amplicon were done using a mix of cDNAs. In addition, the specificity of each primer pair was checked by sequencing the PCR amplicon. The sequences of the primers used are listed in Additional file 1.
cDNAs were synthesized from 2 μg of total RNA to a final reaction volume of 20 μl using a Revert AidTM M-MuLV Reverse Transcriptase (RT) kit according to the manufacturer’s instructions (MBI, Fermentas, Canada). Full-length cDNA synthesis was checked for each sample by PCR amplification of the actin. Quantitative gene expression analysis was carried out by qPCR using a Light Cycler 480 (Roche, Switzerland) as described by Putranto and coll. . Real-time PCR was carried out for eleven housekeeping genes in order to select the most stable gene as the internal control for all the compared tissues (HbelF1Aa, HbUBC4, HbUBC2b, HbYLS8, HbRH2b, HbRH8, HbUBC2a, HbalphaTub, Hb40S, HbUbi, HbActin). HbRH2b was selected as the best reference gene due to its stability in the different tested tissues  (Additional files 2 and 3). The transcript abundance of each gene was relatively quantified by normalization relative to the transcript abundance of the HbRH2b reference gene. All the normalized ratios corresponding to transcript accumulation were calculated automatically by Light Cycler software version 1.5.0 provided by the manufacturer. Heatmap representation was carried out on normalized and centered ΔCt values, using the heatmap2 function of the R software gplots package ,.
qPCR reactions were carried out with 3 biological replicates. The statistical analyses were ANOVAs carried out on raw data after logarithmic transformation. An ad-hoc Tukey HSD (Honestly Significantly Different) test was carried out for the analysis of transcripts in the different organs and different clones. Values with the same letter were not significantly different. For the analysis of transcripts in response to abiotic stress and to hormone treatments, a comparison of means test (Student or Wilcoxon test, depending on the data) was carried out between the control and the treatment at each point of the kinetics. If, at one point, at least one significant difference was found an “s” was indicated, otherwise “ns” was indicated”.
Phylogenetic analysis of JAZgenes
Multiple alignment was carried out on the total protein sequences of the JAZs of Arabidopsis and Hevea. Alignment with Gblocks software  led to the isolation of conserved blocks at least 10 amino acids long. The blocks were then used to construct the phylogenetic tree using PhyML software  which implements a maximum likelihood tree reconstruction method using the LG + gamma model, starting from a BioNJ tree . A RAP-Green analysis was carried out using the original tree from PhyML to predict duplications . The final tree was visualized with the Archaeoptheryx program .
Test of transcriptional activity by transient expression in BY-2 cells of tobacco
Transactivation experiments were carried out following the procedure described by Chaabouni and coll. . The pJAZ_1405(−267) and pJAZ_1405(−955) promoters were cloned to the pMDC107 vector , thereby controlling the GFP reporter gene. The MYC_771 and MYC _94937 genes were cloned under control of the 35S promoter to the pMDC32 vector. Transactivation assay was carried with several controls. First, a window excluding debris and define auto-fluorescence was defined from protoplast solution without transformation. Second, a negative control was obtained by protoplast transformation with the empty reporter vector and effector vector. Third, protoplast transformation with two vectors pJAZ and pHbMYC was carried out. The negative control is used as reference for the calculation of transactivation activity as follows: (pJAZ_1405(−955) + pHbMYC)/(pJAZ_1405(−267) + pHbMYC). This method avoids any risk of disturbance due to the gateway cassette present in pMDC32 vector. The primer sequences used for gateway cloning are listed in Additional file 4. Transformation was replicated 6 times independently. After 16 h, GFP expression was quantified by flow cytometry (FACS Calibur II instrument, BD Biosciences) on the Montpellier Rio Imaging (MRI) platform. Data were analysed using Flowing Software version 2.5.0.
Reads from this library are those published by Duan and coll. (Accession: PRJNA235297 ID: 235297) available on NCBI database.
Identification of the different genes acting in the jasmonate signalling pathway
The different genes acting in the jasmonate signalling pathway were identified from the “comprehensive transcriptome” published by Duan and coll.  using TBLASTN with the corresponding Arabidopsis sequences as the query. For each gene, we selected the one that came out with the best score. For each gene identified in that way, we checked for the conservation of the domains characteristic of each family using INTERPROSCAN. We thus identified 6 contigs corresponding to JAR, 2 for COI, 10 for JAZ and 3 for MYC. The JARs belonged to the GH3 multigene family . GH3s are generally characterized by the presence of 3 small conserved motifs . Motif III was found to be highly conserved in the 6 Hevea sequences. Motifs I and II were found in JAR_5108, JAR_14894 and JAR_59958, while JAR_20347 and JAR_20244 did not display motif I. The absence of motif I in the N terminal part of the proteins deduced from the JAR_20347, JAR_21367 and JAR_20244 contigs was linked to the fact that the contig sequences were incomplete at 5′ (Additional file 5). An analysis of the protein sequences revealed that the two HbCOI, HbCOI_2304 and HbCOI_3058, were characterized by the presence of an F-box domain, along with 3 leucine-rich repeat (LRR) domains (Additional file 6). All of the JAZ proteins identified had the 2 characteristic domains, TIFY and Jas (Additional file 7) . HbMYC_424, HbMYC_771 and HbMYC_94937 all had a bHLH DNA binding domain, along with the 4 conserved regions (I to IV) (Additional file 8) . An analysis of the transcriptome of rubber clone PB260 also enabled us to identify the partners HbNINJA_6328 (Additional file 9) and HbTPL_7591 (Additional file 10). HbNINJA displayed 46% of identical residues with At4g28910, while HbTPL displayed very strong homology with At1g15750 as 85% of the amino acids were identical. We were also able to identify an orthologue of AtMED25, HbMED25_16787, which displayed 50% identity (Additional file 11).
Expression profile of the different genes acting in different developing tissues
Regulationby abiotic stress of genes acting in the jasmonate pathway
Genotypic regulation of genes involved in the JA pathway in response to harvesting stress in mature trees
Clonal regulation of genes acting in the jasmonate signalling pathway
Conservation of the structure HbJAZ genes and that of their Arabidopsisorthologue
Alternative splicing of HbJAZis regulated by tapping stress
MYC_771 and MYC_94937 regulate the transcription of JAZ_1405
Laticifer cells display a transcript pattern for genes acting in the jasmonate pathway that differs from the other tissues
Number of identified members of JAR, COI and JAZ genes in the rubber tree, rice, Arabidopsis , poplar, grapevine and Brachypodium
Number of genes (data from http://rice.plantbiology.msu.edu)
Laticifers cells displayed an original signature of transcripts for the JA signalling pathway since they stood out from all the other tissues tested (Figure 1). Transcript analyses, obtained on PB260, confirmed the results published by Peng and coll. on RRIM 600  showing that HbCOI_2304 is preferentially expressed in latex. In addition, HbCOI_3058 displayed a similar profile (Figure 1). In clone RY-7-33-97, Zhao and coll. showed that the transcripts of HbMYC1 and HbMYC2 were preferentially accumulated in latex . Our results, obtained on clone PB 260 confirmed that tendency (Figures 1 and 2). However, our results did not confirm an abundance of MYC_424 transcripts in response to JA observed in clone RY-7-33-97  (Figure 2E). To date, no study has shown the potential implication of JAZs in the laticifer metabolism. An analysis of the HbJAZ expression profile showed that the transcripts of 5 HbJAZs were more highly accumulated in latex than in the other tissues. For instance, in addition to the transcripts of COI, JAZ and MYC, the transcripts of the JAR_59958 and JAR_20347 genes were highly accumulated in this tissue. All these results suggested that the jasmonate signalling pathway in laticifer cells involved specific actors. This confirmed the importance of studying this pathway in latex production but also in response to harvesting stress.
Harvesting stress can take both common and distinct wounding and dehydration pathways
Latex harvesting amounts to strong abiotic stress that can lead to a physiological syndrome such as TPD. A study of transcript abundance in response to wounding, dehydration, and to hormonal treatments, ethylene and jasmonate, helped to determine what types of abiotic stress and signalling pathways occurred during tapping. The jasmonate signalling pathway was regulated by all the types of stress tested, suggesting the involvement of that pathway in the response to each of the types of stress. Although the comparison was difficult, as the tissues and times tested were not exactly the same, our results confirmed that the transcript abundance of HbMYC1 and HbMYC2, corresponding to MYC_424 and MYC_771, decreased after 6 h of MeJA treatment, then rose from 24 h onwards  (Figure 2E). The results suggested that the signalling pathways of abiotic and harvesting stress may activate the same genes. Indeed, JAZ_863, repressed by ethylene in the stem and by ethephon in bark, was at the same time induced by dehydration and tapping (Figures 2D and 3). In addition, JAZ_29511 and JAZ_14313 were induced by both wounding and tapping, while JAZ_1229 was induced by dehydration and tapping (Figures 2 and 3). Despite that, the results in this study suggested that some independent wounding, dehydration and ethylene pathways were activated during latex harvesting. Indeed, JAZ_2001, JAZ_14313 and JAZ_26925 were induced by ethylene at 24 h, 8 h and 1 h respectively, but were repressed by ethephon in bark (Figures 2 and 3). In latex, the transcripts of COI_2304, MYC_424 and MYC_771 were accumulated in response to tapping (Figure 3), which confirmed the results in the literature ,. Nevertheless, JAZ members are functionally redundant to some extent - and the diversity in their structures suggests specific roles for some of them. This hypothesis is corroborated by the diverse expression patterns displayed by HbJAZ in response to various types of abiotic stress.
HbMYC_771 and MYC_94937 can regulate the HbJAZ genes containing a G-box type cis-element
In addition to negative regulation of JAZs on MYCs, it has been shown that there exists a positive regulation of JAZ transcription by MYCs via the G-box cis-element . Hierarchical clustering grouped MYC_771, MYC_424, JAZ_1405 and JAZ_17062 in the same cluster (Figure 1). Given that the transcripts of MYC_424 and JAZ_17062 were not significantly regulated by jasmonate, we focused on the regulation of JAZ_1405 by MYC_771 and MYC_94937 which, in response to JA, displayed the same expression profile (Figure 2). Transactivation experiments showed that the 2 MYC factors tested were able to regulate the transcription of JAZ_1405 (Figure 7). It is highly likely that this activation of JAZ_1405 by MYC factors occurs via the G-box present in the promoter of that gene. Among the promoters isolated from scaffold sequences, we were able to show that the promoters of HbJAZ_1229 and HbJAZ_19967 also possessed a G-box, suggesting transcriptional regulation of these 2 JAZs by MYCs. This last result may explain the grouping of MYC_771 and JAZ_1405 in the same cluster, but also a similar expression profile for MYC_94937 and JAZ_1405 in response to JA.
JAZ_1229 and JAZ_1660are regulated by alternative splicing in the laticifer cells of tapped trees
The regulation of alternative splicing provides flexibility at transcriptome and proteome level, which helps plants adapt to their environment . However, while the misregulation of alternative splicing has been associated with many human diseases, its biological relevance in plant systems is just beginning to be decipher . Many studies have shown the importance of AS and splicing factors (SF) in the response to abiotic stress (for review, ). With the alternative splicing of JAZ proteins, recent studies suggest that it makes it possible to establish a negative feedback loop to attenuate the response to JA in the event of over-stimulation of the signalling pathway ,. To date, this regulation of JAZs has never been linked to the response to abiotic stress. An analysis of the structure of HbJAZs, along with the sequencing results, confirmed the existence of alternative splicing of the HbJAZ_1229 and HbJAZ_1660 genes (Figure 5). An analysis of the exon/intron junction of these 2 HbJAZs showed that this splicing led to the introduction of a premature termination codon (PTC). In Arabidopsis, the introduction of that PTC leads to the production of a JAZ protein, whose jas domain is absent . In general, the introduction of a PTC engages the transcript in the nonsense-mediated decay (NMD) pathway to degrade it ,. According to the literature, these results suggest that truncated forms of HbJAZ_1229 and HbJAZ_1660 are dominant negative regulators ,,. For the first time, our results brought out a link between the regulation of JAZ alternative splicing and abiotic stress. Indeed, our results showed that alternative splicing of JAZ_1229 and JAZ_1660 could be regulated by tapping in latex. Curiously, that regulation was opposite for the transcripts of JAZ_1229 and JAZ_1660 (Figure 6). An analysis of the abundance of the 2 forms of transcripts of these 2 HbJAZs showed that the transcript abundance of the spliced form remained at least 500 times greater than the non-spliced form (Figure 6). This final observation tallied with what is generally observed in Arabidopsis since, although intron retention is the most common form of AS (~40%), many of these transcripts are not very abundant at all . Taken together these results suggested a compensatory phenomenon and functional redundancy of HbJAZ_1229 and HbJAZ_1660, which is all the more likely in that they were classed in the same cluster (Figure 1).
Genes acting in the JA pathway are expressed differentially in the latex of different Heveaclones
The results presented here show that the JA signalling pathway was regulated differently depending on the clones tested. Indeed, the negative JAZ regulators were over-expressed in PB260, while the transcripts of MYC factors and the JAR enzyme, which are positive regulators of the JA pathway, were accumulated preferentially in clones INC 53 and RRIM600 (Figure 4). These results suggested activation of the JA target genes in clones with a slow laticifer metabolism, more resistant to TPD.
The identification of signalling pathways involved in TPD resistance should make it possible to isolate the master regulators controlling resistance to this syndrome. The identification of JA transduction pathway members and knowledge of their expression pattern open up new ways of improving the TPD-tolerance of Hevea clones. The JA signalling pathway is very widely distributed and very highly conserved during evolution. However, a study on extra floral nectar (EFN) excretions by central American acacias revealed that resistance to biotic stress via the jasmonate pathway might be induced or constitutive in some phylogenetically very close species . Thus, that study suggests that specific variability of the JA pathway may have some major consequences for resistance to stress.
The present study provides some molecular clues on how the Jasmonate pathway can be involved in harvesting stress in Hevea brasilliensis through (i) the specific expression pattern of jasmonate pathway actors in latex, (ii) their transcriptional regulation in response to harvesting stress, (iii) differential expression depending on the Hevea clone, (iv) their putative alternative splicing regulation in response to harvesting. A better understanding of transcriptional regulations during harvesting stress, along with the use of clonal diversity in response to such stress, are therefore a major challenge for improving resistance to stress and rubber production in Hevea.
Availability of supporting data
The authors confirm that all data underlying the findings are fully available without restriction. Character Matrix and phylogenetic tree have been deposited in treebase (ID: 16569) and data are available at the following URL: http://purl.org/phylo/treebase/phylows/study/TB2:S16569.
This work was supported by CIRAD. We are grateful to Prof. Songnian Hu from Beijing Institute of Genomics for access to the Hevea genome sequences. The authors also thank Peter Biggins for the English version of this manuscript.
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