Differential gene expression indicates involvement of F-box proteins and E3 ligases in sexual versus apomictic germline specification in Boechera.

Germline specification is the first step during sexual and apomictic plant reproduction. This takes place in a specialized domain of the reproductive flower tissues, the nucellus of the ovule. In each case, a sporophytic cell is determined to initiate germline development. These cells, the megaspore mother cell (MMC) or apomictic initial cell (AIC) in sexual plants and apomicts, respectively, differ in their developmental fate. While the MMC undergoes meiosis, the AIC aborts or omits meiosis to form the female gametophyte. Although these distinct developmental processes have long been described, little is known about the gene regulatory basis involved. To elucidate gene regulatory networks underlying sexual and apomictic germline specification, we conducted tissue-specific transcriptional profiling using laser-assisted microdissection and RNA-Seq. We compared the transcriptomes of the nucellar tissues harbouring the MMC or AIC between different accessions of Boechera. The six accessions we used represented four species and two ploidy levels, allowing us to distinguish between differences in gene expression caused by the genetic background or the reproductive mode. Comparative data analysis revealed widely overlapping gene expression patterns in apomictic versus sexual Boechera accessions. Nevertheless, 45 significantly differentially expressed genes were identified, which potentially play a role for determination of sexual versus apomictic reproductive mode. Interestingly, based on annotations, these include F-box proteins and E3 ligases that might relate to genes previously described as regulators important for sexual or apomictic reproduction. Thus, our findings provide new insight into the transcriptional basis of sexual and apomictic germline specification.