DNA methylome and transcriptome landscapes revealed differential characteristics of dioecious flowers in papaya

Separate sexes in dioecious plants display different morphology and physiological characteristics. The differences between the two sexes lie in their highly differentiated floral characteristics and in sex-related phenotype, which is genetically determined and epigenetically modified. In dioecious papaya (Carica papaya L.), global comparisons of epigenetic DNA methylation and gene expressions were still limited. We conducted bisulfite sequencing of early-stage flowers grown in three seasons (spring, summer and winter) and compared their methylome and transcriptome profiles to investigate the differential characteristics of male and female in papaya. Methylation variances between female and male papaya were conserved among three different seasons. However, combined genome-scale transcriptomic evidence revealed that most methylation variances did not have influence on the expression profiles of neighboring genes, and the differentially expressed genes were most overrepresented in phytohormone signal transduction pathways. Further analyses showed diverse stress-responsive methylation alteration in male and female flowers. Male flower methylation was more responsive to stress whereas female flower methylation varied less under stress. Early flowering of male papaya in spring might be associated with the variation in the transcription of CpSVP and CpAP1 coinciding with their gene-specific hypomethylation. These findings provide insights into the sex-specific DNA methylation and gene expression landscapes of dioecious papaya and a foundation to investigate the correlation between differentiated floral characteristics and their candidate genes.