Identification of candidate genes involved in determining pollen-grain aperture morphology by comparative transcriptome analysis in Papaveraceae Ismael Mazuecos-Aguilera, Víctor N. Suárez-Santiago Manuscript in. undefined

Background and Objectives Pollen apertures, areas of the wall where the exine is weakened or absent, are extremely varied in shape, number, and position. In terms of shape, apertures can be elongated or round, both types being present in all taxonomic groups of angiosperms and each being more adapted to certain environmental conditions. In the last decade, certain genes involved in the formation of pollen apertures have been discovered. However, only one protein family (ELMOD) has been found in Arabidopsis, which acts upstream of the aperture-formation pathway. In this protein family, the interaction of one of its members, ELMOD_E, with two others, MCR/ELMOD_B and ELMOD_A, can change the morphology of apertures from colpus (elongated) to pore (round). Here, comparative transcriptome analysis between two pairs of taxa with different aperture morphology is used in an attempt to identify candidate genes involved in the determination of pollen-aperture morphology in Papaveraceae (order Ranunculales). Methods In this study, two pairs of Papaveraceae species belonging to two different subfamilies were used. Within each pair, one species has colpate pollen and the other porate (Fumarioideae: Dactylicapnos torulosa, 6-colpate and Fumaria bracteosa, pantoporate; Papaveroideae: Eschscholzia californica 5-7 colpate and Roemeria refracta, 6-porate). The transcriptome of the colpate and porate pollen was sequenced and compared when the pollen was in the tetrad development stage, the time at which aperture formation begins. Differentially expressed genes (DEGs) between the two groups and not differentially expressed within each group, which could potentially be involved in aperture shape determinism, were selected. The expression level of four genes was validated by qRT-PCR to confirm their differential expression. Key Results A total of 531 DEGs were found between the colpate and porate pollen species groups that are not differentially expressed within each group. The expression levels determined by qRT-PCR validate those measured by transcriptome analysis. Among the DEGs, no member of the ELMOD family was found, this being the only family discovered so far that could be involved in determining the shape of pollen-grain apertures. However, genes related to the formation of the callose wall or the organization of the cytoskeleton were found, these processes being involved in the formation of the apertures. Conclusions The results provide a list of genes that could determine the shape of the apertures in Papaveraceae. These results open new avenues for functional studies of these genes to confirm their involvement in this process.