Spatiotemporal regulation of anther's tapetum degeneration paved the way for a reversible male sterility system in cotton.

Male sterility is an important agronomical trait in self-pollinating plants for producing cost-effective F1 hybrids to harness the heterosis. Still, large-scale development and maintenance of male sterile lines and restoring fertility in F1 hybrids pose significant challenges in plant hybrid breeding. Cotton is a self-pollinating crop and exhibits strong hybrid vigor. However, there are currently few breeding methods to achieve cost-effective production of F1 hybrid cotton. Here, we utilized novel functions of the Arabidopsis autophagy-related BECLIN1/ATG6 and a mutant of E3 ubiquitin ligase COP1 (COP1) genes in developing rescuable male sterility in cotton. We have generated multiple male-sterile (MS) and restorer (RS) cotton lines expressing BECLIN1 and COP1, respectively. Cytological observation showed that post-meiotic tapetal expression of BECLIN1 delays tapetum developmental programmed cell death (dPCD) by affecting reactive oxygen species (ROS) balance-this delay in dPCD results in early microspore defects and later small-sized flowers with indehiscent anthers. Furthermore, the evaluation of F1 hybrids developed by crossing MS and RS lines showed that early tapetal COP1 expression abolishes expression of BECLIN1 resulting in normal tapetum degeneration, pollen development, and fertility. In addition, the F1 hybrid developed with MS and RS cotton lines in transgenic glass-house and net-house conditions showed the rescued fertility comparable with control plants (WT). In terms of cotton fiber productivity, the COP1-expressing transgenic cotton lines outperformed the WT. The current work effectively demonstrates the wider applicability of the new F1 cotton production system.