ABA is involved in XsMYB30-mediated leaf wax accumulation and drought resistance in yellowhorn

Yellowhorn (Xanthoceras sorbifolium) is an excellent economic tree species in northern China, but its main distribution area often suffers from drought stress, which seriously affects its yield and the expansion of suitable growth area. The increase of ABA content and wax accumulation in plants are both measures to cope with drought stress, but the interaction mechanism between ABA and wax is currently unclear. We found that the high wax variety ‘Zhongshi 4’ has higher ABA level compared with the low-wax variety, and the XsMYB30 transcription factor which can positively regulate leaf wax synthesis was also up-regulated in the high-wax variety. Therefore, in this study, we analyzed the relationship between ABA and XsMYB30 in the wax accumulation of yellowhorn. It was found that ABA synthesis inhibitor reduced the deposition of wax on the leaves of yellowhorn. Moreover, overexpression of XsMYB30 increased the ABA contents, affecting the stomatal aperture in response to drought. Biological analysis confirmed that XsMYB30 could directly bind to the promoter of XsNCED3 and promote its expression. We further showed that the inhibition of the ABA level resulted in the reduced wax accumulation and weakened drought resistance in XsMYB30 overexpression lines. Our research indicates that ABA plays an important role in XsMYB30-mediated cuticular wax accumulation and drought resistance, and provides new insights into the underlying mechanism between ABA and wax.