Auxin Biosynthesis By The YUCCA Flavin Monooxygenase Is Critical For Pollen Grain Development

Auxin, the earliest discovered plant hormone, participates in a variety ofphysiological and developmental processes in plants, such as plant cell elongationand division, vascular tissue development, plant geotropism and phototropismformation, apical dominance, as well as the growth of floral organs. Indole-3-aceticacid (IAA) has been recognized as the major auxin. YUCs genes encoding flavinmonoxygenase are considered the main IAA biosynthesis pathway in Arabidopsis. Thedouble mutant of yuc2yuc6showed male sterile phenotype. On the basis of theprevious work, we investigated the detailed developmental defects of yuc2yuc6. Thecross-sections showed that the abortion of yuc2yuc6microspores happened afterstage9. TEM examination validated pollen wall development in yuc2yuc6was notaffected, but the microspores were severely vacuolated and without any cytoplasmiccontent. DAPI staining of yuc2yuc6microspores showed that pollen grains exhibiteddispersed nucleus after asymmetric mitotic division indicating that pollen mitosis I isaffected in yuc2yuc6. Microarray analysis of yuc2yuc6buds showed that a largenumber of genes were down-regulated including cell cycle and DNA synthesisregulated genes. Futhermore, down-regulated genes in arf17mutant showed anoverlap with that in yuc2yuc6, suggesting that ARF17may function downstream ofYUC2and YUC6to regulate pollen mitosis I. Collectively, our findings provide newevidences of regulatory role of auxin for anther development.