PcMYBs responded to 6-BA to regulate PcCKXs to promote germination of primary rhizome buds of Polygonatum cyrtonema Hua.

Polygonatum cyrtonema Hua is valued both as a precious traditional Chinese medicinal herb and as a prime example of a plant that bridges medicinal and culinary applications. Renowned for its significant medicinal and edible qualities, this botanical exemplifies a unique convergence of therapeutic and nutritional benefits. However, the primary rhizome of Polygonatum cyrtonema Hua development is difficult to germinate into seedlings in the same year. The germination of primary rhizome buds of P. cyrtonema can be promoted by treatment with exogenous hormone 6-BA, but the related regulatory mechanism is not clear. In this study, we found that the cytokinin oxidase (CKX) plays a key role in the germination of primary rhizome buds of P. cyrtonema. PcCKX1,2,3 promoted the expression of dormancy positively regulated genes, and repressed the expression of dormancy negatively regulated genes, which in turn inhibited Arabidopsis seed germination, and PcCKX2 was the major gene. PcCKX1,2,3 promoted the expression of dormant positively regulated genes such as sweet potato IbZEP, IbNCED3, IbDOG1, IbABI5, IbCKX3, and IbCKX7, which in turn delayed the sprouting of sweet potato rhizomes, and that PcCKX2 played a major role. We further screened three MYB transcription factors significantly associated with PcCKX1,2,3. Yeast one-hybrid, Dual-LUC, and EMSA experiments showed that PcMYB4, PcKUA1, and PcCSA all bind to and repress the expression of elements of the PcCKX1,2,3 promoter. Heterologous transformation of Arabidopsis experiments showed that PcMYB4, PcKUA1, and PcCSA repressed the expression of dormancy-associated genes such as DOG1, NCED3, ABI5, CKX3, and CKX7, which, in turn, facilitated Arabidopsis seed germination. Taken together, we found that PcMYBs are involved in the transcriptional regulation of PcCKXs to promote the germination of primary rhizome buds of P. cyrtonema. The results of this study lay the foundation for analyzing the molecular mechanism of primary rhizome bud germination in P. cyrtonema.