Abstract
Genetic determination of gender is a fundamental developmental and evolutionary process in plants. Although it appears that dioecy in Populus is partially genetically controlled, the precise gender-determining systems remain unclear. The recently-released second draft assembly and annotated gene set of the Populus genome provided an opportunity to re-visit this topic. We hypothesized that over evolutionary time, selective pressure has reformed the genome structure and gene composition in the peritelomeric region of the chromosome XIX which has resulted in a distinctive genome structure and cluster of genes contributing to gender determination in Populus. Multiple lines of evidence support this working hypothesis. First, the peritelomeric region of the chromosome XIX contains significantly fewer single nucleotide polymorphisms than the rest of Populus genome and has a distinct evolutionary history. Second, the peritelomeric end of chromosome XIX contains the largest cluster of the nucleotide-binding site-leucine-rich repeat (NBS-LRR) class of disease resistances genes in the entire Populus genome. Third, there is a high occurrence of small microRNAs on chromosome XIX coincident to the region containing the putative gender-determining locus and the major cluster of NBS-LRR genes. Further, by analyzing the metabolomic profiles of floral bud in male and female Populus trees using a gas chromatography-mass spectrometry, we found there are gender-specific accumulations of phenolic glycosides. Taken together, these findings provide new insights into the genetic control of gender determination in Populus.
