The cotton pectin methyl esterase gene GhPME21 functions in microspore development and fertility in Gossypium hirsutum L.

Pectin widely exists in higher plants' cell walls and intercellular space of higher plants and plays an indispensable role in plant growth and development. We identified 55 differentially expressed genes related to pectin degradation by transcriptomic analysis in the male sterile mutant, ms1. A gene encoding pectin methylesterase (GhPME21) was found to be predominantly expressed in the developing stamens of cotton but was significantly down-regulated in ms1 stamens. The tapetal layer of GhPME21 interfered lines (GhPME21i) was significantly thickened compared to that of WT at the early stage; anther compartment morphology of GhPME21i lines was abnormal, and the microspore wall was broken at the middle stage; Alexander staining showed that the pollen grains of GhPME21i lines differed greatly in volume at the late stage. The mature pollen surfaces of GhPME21i lines were deposited with discontinuous and broken sheets and prickles viewed under SEM. Fewer pollen tubes were observed to germinate in vitro in GhPME21i lines, while tiny of those in vivo were found to elongate to the ovary. The seeds harvested from GhPME21i lines as pollination donors were dry and hollow. The changes of phenotypes in GhPME21i lines at various stages illustrated that the GhPME21 gene played a vital role in the development of cotton stamens and controlled plant fertility by affecting stamen development, pollen germination, and pollen tube elongation. The findings of this study laid the groundwork for further research into the molecular mechanisms of PMEs involved in microspore formation and the creation of cotton male sterility materials.