The S_C10-RNase promoter displays changes in DNA methylation patterns through pistil development in self-incompatible...

In Solanaceae, self-incompatibility is a genetic mechanism that prevents endogamy in plant populations. Expression of the S-determinants, S-RNase, and SLF, is tightly regulated during pistil and pollen development. However, the molecular mechanism of gene expression regulation in S-RNase-based self-incompatibility systems must be better understood. Here, we identified a 1.3 Kbp sequence upstream to the coding region of the functional S_C10-RNase allele from the self-incompatible Nicotiana alata, which directs S_C10-RNase expression in mature pistils. This S_C10-RNase promoter includes a 300 bp region with minimal elements that sustain the S_C10-RNase expression. Likewise, a fragment of a transposable element from the Gypsy family of retrotransposons is also present at the -320 bp position. Nevertheless, its presence does not affect the expression of the S_C10-RNase in mature pistils. Additionally, we determined that the S_C10-RNase promoter undergoes different DNA methylation states during pistil development, being the mCHH methylation context the most frequent close to the transcription start site at pistil maturity. We hypothesized that the Gypsy element at the S_C10-RNase promoter might contribute to the DNA methylation remodeling on the three sequence contexts analyzed here. We propose that mCHH methylation enrichment and other regulatory elements in the S-RNase coding region regulate the specific and abundant S_C10-RNase expression in mature pistils in N. alata.