Evolution of sex‐determination in dioecious plants: From active Y to X/A balance?

Abstract

Sex chromosomes in plants have been known for a century, but only recently have we begun to understand the mechanisms behind sex determination in dioecious plants. Here, we discuss evolution of sex determination, focusing on Silene latifolia, where evolution of separate sexes is consistent with the classic “two mutations” model—a loss of function male sterility mutation and a gain of function gynoecium suppression mutation, which turned an ancestral hermaphroditic population into separate males and females. Interestingly, the gynoecium suppression function in S. latifolia evolved via loss of function in at least two sex‐linked genes and works via gene dosage balance between sex‐linked, and autosomal genes. This system resembles X/A‐ratio‐based sex determination systems in Drosophila and Rumex, and could represent a steppingstone in the evolution of X/A‐ratio‐based sex determination from an active Y system.

Sex chromosome cycle as a mechanism of stable sex determination

“…The X carries GSFX , a gametolog of GSFY that has undergone non-functionalization, suggesting that the non-functionalization of the X copy played a role in establishing the sex determination system. Notably, SlWUS1 , an ortholog of Arabidopsis WUSCHEL, which promotes the enlargement of the gynoecium, is in stratum 1 of the X but is absent from the Y ( 48 , 76 ) . This observation indicates that the X functions in sex determination and female enlargement, suggesting that X chromosome evolution led to improved female fitness.…”

“…This observation indicates that the X functions in sex determination and female enlargement, suggesting that X chromosome evolution led to improved female fitness. Furthermore, even if GSFY were to become non-functional, sex determination could still be achieved by altering the activity of SlWUS1 , which may be an excellent example of a mechanism to avoid the loss of female fitness ( 76 ) .…”