Filament elongation and pollen development regulated by auxin is crucial for male fertility in Arabidopsis

The flavin monooxygenase encoded by YUCCA (YUC) is the rate-limiting enzyme in auxin biosynthesis, and its spatiotemporal expression regulates local auxin biosynthesis, resulting in a dose-dependent regulation of flower development. Previous research reported that decreased fertility in yuc2yuc6 double mutant was caused by abnormal development of pollen. In this study, we found that yuc2yuc6 showed different fertility between early (growth stage 6.10–6.30) and late (growth stage 6.5–6.9) flowering stages, but the reason was still unclear. At early flowering stage, the shrunken pollen was aborted which could be recovered after overexpressing iaaM. The ratio of shrunken pollen decreased since most pollen grains showed normal shape at late flowering stage. The siliques were pumped and filled with seeds after artificial pollination (yuc2yuc6♂ × WT♀), that means the pollen was viable for pollination at late flowering stage. Filaments were short at early flowering stage while some filaments were normal at the late flowering stage. In conclusion, the yuc2yu6 was almost sterile due to the aborted pollen and short filaments at early flowering stage. The shorter filaments might prevent the completion of pollination in space distance at early flowering stage. Along with the growth of yuc2yuc6, some filaments and pollen shape recovered that ensured normal pollination at late flowering stage. Compensatory expression of YUC4/7/9/11 resulted in the partial recovery of filament length and pollen shape/vitality at late flowering stage in yuc2yuc6. We speculate that auxin determines fertility by spatiotemporally regulating the filament elongation and pollen development, mediated through the expression of functional redundant YUCs in Arabidopsis. This discovery provides deeper insights into the protective mechanisms underlying plant reproductive resilience.