Abstract
For centuries, scientists have been intrigued by the origin of dioecy in plants, characterizing sex-specific development, uncovering cytological differences between the sexes, and developing theoretical models. Through the invention and continued improvements in genomic technologies, we have truly begun to unlock the genetic basis of dioecy in many species. Here we broadly review the advances in research on dioecy and sex chromosomes. We start by first discussing the early works that built the foundation for current studies and the advances in genome sequencing that have facilitated more-recent findings. We next discuss the analyses of sex chromosomes and sex-determination genes uncovered by genome sequencing. We synthesize these results to find some patterns are emerging, such as the role of duplications, the involvement of hormones in sex-determination, and support for the two-locus model for the origin of dioecy. Though across systems, there are also many novel insights into how sex chromosomes evolve, including different sex-determining genes and routes to suppressed recombination. We propose the future of research in plant sex chromosomes should involve interdisciplinary approaches, combining cutting-edge technologies with the classics to unravel the patterns that can be found across the hundreds of independent origins.
Highlights
Across land plants exists an amazing variety of strategies for sexual reproduction [1].Species have independently evolved self-incompatibility loci [2], temporal variation in flower development [3,4], and spatial distancing of male and female organs on the same plant [5,6,7], among many others [1]
A candidate list of floral genes has been developed in D. rotundata [129], but more in-depth analyses are needed to identify those involved in sex determination
Tapetal Development and Function 1 (TDF1) develop functional ovaries, but non-functional anthers [50]. Together these results show that Suppressor of Female Function (SOFF) and TDF1 are the female and male-sterility genes, respectively, in A. officinalis
Summary
Across land plants exists an amazing variety of strategies for sexual reproduction [1]. In haploid-dominant plants, like bryophytes, dioecious species with genetic sex determination have UV sex chromosomes, with the inheritance of a U correlating with female gametic sex expression and a V with male [13,15]. Though some species have multiple sex chromosomes (e.g., XY1 Y2 or U1 U2 V) [8,16,17,18], which can occur through structural changes like chromosomal fusions and fissions or through polyploidy These differences in heterogamety and ploidy of sex chromosomes found across land plants are powerful for contrasting the evolutionary processes that impact these genomic regions, especially as the mechanisms of sex determination on sex chromosomes have expanded beyond the classic two-locus model [19]. We conclude with future directions in plant sex chromosome evolution research
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