Developmental pathways underlying sexual differentiation in the U/V sex chromosome system of giant kelp
Daniel Liesner, Guillaume Cossard, Min Zheng, Olivier Godfroy, Josué Barrera‐Redondo, Fabian B. Haas, Susana M. Coelho
Abstract
In many multicellular organisms, sexual development is not determined by XX/XY or ZW/ZZ systems but by U/V sex chromosomes. In U/V systems, sex determination occurs in the haploid phase, with U chromosomes in females and V chromosomes in males. Here, we explore several male, female, and partially sex-reversed male lines of giant kelp to decipher how U/V sex chromosomes and autosomes initiate male versus female development. We identify a key set of genes on the sex chromosomes involved in triggering sexual development and characterize autosomal effector genes underlying sexual differentiation. We show that male, but not female, development involves large-scale transcriptome reorganization with pervasive enrichment in regulatory genes, faster evolutionary rates, and high species-specificity of male-biased genes. Our observations imply that a female-like phenotype is the “ground state”, which is complemented by the presence of a U-chromosome but overridden by a dominant male developmental program triggered by the V-chromosome. • Identification of the genetic basis of haploid male and female kelp development • Enrichment of fast-evolving regulatory genes underlies male-specific development • Male development requires large-scale rewiring of a female-like ground state Exploring male, female, and partially sex-reversed male lines of giant kelp with U/V sex chromosomes, Liesner et al. identify key genes and developmental programs in haploid sex determination. Only male developmental fate involves large-scale transcriptome reorganization, implying that a female-like phenotype is the “ground state” of giant kelp gametophyte morphology.