CmWOX2 modulates somatic embryogenesis in Chinese chestnut (Castanea mollissima Blume)

Chinese chestnut (Castanea mollissima Blume) is distinguished by its remarkable nut quality and robustness against disease and environmental stressor. However, its somatic embryogenesis process is notably slow, presenting a significant bottleneck in its cultivation. This study focuses on the WUSCHEL (WUS)-related homeobox 2 gene (WOX2), a member of WOX transcription factors gene family, known for its critical role in the somatic embryo development of Arabidopsis. We have identified and explored the function of a WOX2 homolog in Chinese chestnut, termed CmWOX2, in the context of somatic embryogenesis. Our analysis revealed seven WUS gene family members in the species, with CmWOX2 being uniquely upregulated in callus. Our experiments demonstrated that suppression of CmWOX2 expression diminishes somatic embryo production, whereas its overexpression enlarges the embryonic callus diameter. Notably, CmWOX2 expression levels are threefold higher in varieties with high embryogenic competence, such as 'Jingshuhong' and 'Huaihuang', compared to those with lower competence, including 'Jiujiazhong' and 'Shandonghongli'. These findings underscored the pivotal role of CmWOX2 in the initial stages of Chinese chestnut somatic embryogenesis, highlighting its potential as a target for enhancing somatic embryogenesis in this species.