The role and mechanism of TgCWIN2-mediated changes of photo-assimilates in modulating early development of Torreya grandis seeds

Early seed development is vital for plant reproduction, but the processes behind this in gymnosperms like Torreya grandis, which has a low rate of normal early-developed seeds, are not well understood. To fill this knowledge gap, we embarked on a comprehensive investigation encompassing the morphology and phenology of seed development in T. grandis. Using the ¹³C labelling analysis, coupled with leaf removal and seed thinning treatments, we observed a substantial increase in the content of photo-assimilate, an almost 10% increase in sucrose content under seed thinning treatments, thereby leading to an increase in the proportion of normal early-developed seeds, reaching 15%. Concurrently, through the integration of multi-omics analyses and transient overexpression validation, we identified cell wall invertase coding gene, TgCWIN2, which plays a pivotal role in sucrose cleavage during the early development of T. grandis seeds. Further gene co-expression, dual-luciferase assay, and yeast one-hybrid assay revealed that TgWRKY31 was a candidate regulator of TgCWIN2, positively influencing its expression by direct binding to the TgCWIN2 promoter. Notably, TgWRKY31 transient overexpression substantially enhances the expression of TgCWIN2, thereby contributing to a higher proportion of normal early-developed seeds. Our findings not only provide a comprehensive understanding of the underlying mechanisms governing the early development of T. grandis seeds, but are also essential for establishing strategies to enhance early seed development and improve yield.