Fig. 1

Microspore development stages sampled for RNA sequencing analysis. Brightfield micrographs of representative samples from three microspore stages. All bars represent 20 μm. Arrowheads point to cells with morphological characteristics that meet our criteria for manual cell selection. a Untreated vacuolated microspores at uninucleate stage (S1); manually selected microspores were characterized by a large central vacuole and a clear cytoplasm. b Microspores with star-like structure after 10-days cold stress pre-treatment (S2); microspores are slightly enlarged after stress induction, the vegetative nucleus migrates into the center of the cell, the cytoplasm becomes structured and shows cytoplasmic strands, the so-called “star-like structure”. c Microspores undergoing first nuclear division (S3); the vegetative nucleus is centrally located and has divided