Mechanism of light induced shoot regeneration from rhizome in Cymbidium aloifolium

• The experimental system of shoot regeneration not depended on exogenous hormone was established in Cym. aloifolium . • Shoot differentiate induced by light is mainly due to the increase of endogenous cytokinin, however, the role of light cannot be replaced by exogenous cytokinin. • Light rapidly creates a high cytokinin/auxin ratio microenvironment and up-regulates the expressions of WUS and PIN1 to initiate shoot regeneration. • Light increases the contents of endogenous IAA and cytokinin through regulating the expressions of relative genes and promotes shoot formation. Light is essential for shoot regeneration in plant tissue culture, but the mechanism of light-induced shoot regeneration is still unclear. In this study, we found the rhizomes of Cymbidium. aloifolium were not able to regenerate shoots under dark condition, but quickly differentiated into seedlings on hormone-free medium under light. Supplement of 6-BA accelerated shoot regeneration, while supplement of lovastain completely inhibited shoot regeneration, in contrast, additive of NAA, NPA and BBO only delayed shoot regeneration, indicating that cytokinin played key role in shoot regeneration. However, rhizomes cultured on MS medium with cytokinin under dark condition did not produced shoots, which illustrated that the function of light on shoot regeneration could not be replaced by exogenous cytokinin. During shoot regeneration, the content of cytokinin in rhizomes cultured under light was significantly increased through upregulating the expression level of LOG7 and down-regulating the expression level of CKX9 compared with that under dark condition except for the first day,when the ratio of IAA/cytokinin was significantly lower, and the expression levels of PIN1 and WUS were significantly higher in rhizomes cultured under light than that of the control. These results demonstrated that light induced shoot regeneration by regulating the expressions of related genes expression and promoting the formation of polarity and inner micro-environment of high cytokinin/auxin ratio. Our results are helpful for further research on molecular mechanism of light-induced shoot regeneration and establishing efficient micropropagation system in Cymbidium .