Progress on sex determination of dioecious plants

Abstract

Background & Aims: Sexual differentiation of plants, also known as dioecy, is the phenomenon of the different female and male reproductive organs in different species and individuals. Dioecious species of flowering plants evolved independently into multiple phylogenetic branches, with each expressing different sex chromosome status, sex determination regions and genes for each branch. In this review, we will summarize the current direction of sex determination research in angiosperms, and appropriately prospect the direction of future research. Progress: We summarized the formation process of the plant sex determining gene model and the evolution of plant sex chromosomes after conducting a literature review. Two types of mutation models for plant sex determination have been proposed: The ‘two-mutations’ model clarifies that the evolution of sex determination requires two mutations, leading to male sterility and female sterility respectively, while the ‘single-mutation’ model is a single mutant gene that regulates and determines both male and female development of the plant. The diversity of plant sex chromosomes and sex determination systems provides an excellent opportunity to study the formation mechanism of plant sex-related genes, sex determination regions, and sex chromosome evolution. The evolution of plant chromosomes started with a pair of autosomes producing sex-determining gene mutations, forming the initial sex chromosomes. With different selection pressure between female and male plant individuals, the mutant genes were gradually antagonized, and the recombination inhibition was promoted. Accumulation of repeated elements and inhibition of recombination causes the Hill-Robertson effect, which increases the difference between the two chromosomes and eventually leads to the formation of sex chromosomes. The sex chromosomes of some species gradually evolved from homomorphic chromosomes to heteromorphic chromosomes. In this review, sex-determined regions and genes are sorted out and compared in detail according to currently existing characteristics. At present, most studies on the sex-determining regions and genes of angiosperms are carried out by methods such as genome, transcriptome, and resequencing, and the results are primarily in line with the ‘two-mutations’ or ‘single-mutation’ models. Meanwhile, this review further outlines the application of sex determination research in practical production. Prospects: We propose four suggestions for future research on sex determination in plants: (1) gradually expanding the sight from gene to the regulatory pathways of research; (2) shifting from a single species to research comparisons of related families and genera; (3) improving and exploring current or new sex-determining gene models or sex-model species; and (4) strengthening the identification technology in actual production research and development efforts.