Genome sequence comparison reveals a candidate gene involved in male–hermaphrodite differentiation in papaya (Carica papaya) trees

Abstract

The sex type of papaya (Carica papaya) is determined by the pair of sex chromosomes (XX, female; XY, male; and XYh, hermaphrodite), in which there is a non-recombining genomic region in the Y and Yh chromosomes. This region is presumed to be involved in determination of males and hermaphrodites; it is designated as the male-specific region in the Y chromosome (MSY) and the hermaphrodite-specific region in the Yh chromosome (HSY). Here, we identified the genes determining male and hermaphrodite sex types by comparing MSY and HSY genomic sequences. In the MSY and HSY genomic regions, we identified 14,528 nucleotide substitutions and 965 short indels with a large gap and two highly diverged regions. In the predicted genes expressed in flower buds, we found no nucleotide differences leading to amino acid changes between the MSY and HSY. However, we found an HSY-specific transposon insertion in a gene (SVPlike) showing a similarity to the Short Vegetative Phase (SVP) gene. Study of SVP-like transcripts revealed that the MSY allele encoded an intact protein, while the HSY allele encoded a truncated protein. Our findings demonstrated that the SVP-like gene is a candidate gene for male-hermaphrodite determination in papaya.