LhMYB93–LhEAT1 module modulated by LhBRG3 regulates tapetum degradation and pollen fertility in lily (Lilium Asiatica. hybrida)

Male sterility is crucial for solving pollen contamination and promoting inter-varietal hybridization. As the innermost layer of the anther, the tapetum directly contacts microspores, and tapetal abnormalities typically lead directly to male sterility. However, the regulatory mechanisms of tapetal degradation and its transport of substances to microspores remain poorly understood. This study identified LhMYB93 as a key positive regulator of tapetum degradation and microspore development in lilies. Specifically, transcriptomic analysis combined with transcriptomic and functional analyses revealed that LhMYB93 is expressed at lower levels in male-sterile lilies, and LhMYB93 can partially restore pollen fertility in male-sterile lilies. Additionally, LhMYB93 interacts with LhEAT1 to effectively activate the transcription of LhABCG26, a gene essential for tapetum degradation and microspore development. Additionally, in vitro and in vivo ubiquitination experiments have demonstrated that the LhEAT1–LhMYB93 module is ubiquitinated by the E3 ubiquitin ligase LhBRG3 during the late stages of anther development (S9–10) and subsequently degraded by the 26S proteasome. This process ensures the normal development and timely degradation of the tapetum, promoting the normal development of pollen. These findings provide novel insights into the regulatory mechanisms governing microspore development following tapetum degradation during lily anther development, expanding the regulatory framework of programmed cell death (PCD) and nutrient transport in tapetum during pollen development in monocotyledons.