Abstract
Papaya is a fruit crop possessing XY sex chromosomes. The development of long male peduncles (Mp) is pivotal for the transition from gynodioecy to dioecy. The gene controlling peduncle length, CpMp, is one of the four genes driving the evolution of stage 3 sex chromosomes in papaya. Here, we identify a Y-specific SVP paralog, CpSVP-Yp, which is validated as CpMp through comparative genomics and complementation tests. CpMp promotes peduncle elongation by activating CpYUC6, increasing auxin levels, which in turn enhance GA levels and stimulate CpGASA6, driving cell division and elongation. Overexpression of CpGASA6 confirms its role and reveals a feedback loop suppressing IAA biosynthesis. We also identify two upstream regulators: CpTRAB1, a GA-repressed activator, and CpGATA8, a CpMp-induced repressor, forming dual feedback circuits. We show that male trees produce 400× more pollen than hermaphrodites, conferring a fitness advantage. Together with two sex determination genes, CpMp is essential for dioecy and sex chromosome evolution in papaya.