Study On The Mechanism Of Arabidopsis Thaliana Auxin Synthesis YUCCA Gene Involved In Regulation Of Male Gametophyte Development

Auxin plays a critical role in anther dehiscence, pollen maturation, and filament elongation, but auxin sources for pollen development is not well defined. YUCCAs genes encoding flavin monoxygenase are involved in the main IAA biosynthesis pathway in Arabidopsis. Previous studies have showed that the loss of function mutant yuc2yuc6 showed a male-sterile phenotype and its pollen grains possess dispersion nucleus after asymmetric mitotic division. Here, we report that besides the morphological phenotypes, YUC2 and YUC6 behave genetically as sporophytic genes required for pollen mitosis I. Consistent with the genetic data, the immunohistochemistry assay showed that YUC2 is mainly expressed in the tapetum, which is a layer of sporophytic cells. We also found that the auxin response was disturbed in yuc2yuc6 mutant as we cannot detect any DR5::GFP signals in the anther of yuc2yuc6. This result means that the IAA was mainly synthesized by YUC2 and YUC6 in anther. Through detailed analyses, we also found that arf17 display similar phenotypes as yuc2yuc6 during the microspore development, suggesting this auxin response factors may regulated by YUC2, 6 proteins and involved in the regulation of PMI process. Our findings demonstrate an essential role of auxin in pollen mitosis and conclude that the microspores in yuc2yuc6 mutants fail to entry into PM I may be results from mis-regulation of the activity of ARFs.