McWRKY43 Confers Cold Stress Tolerance in Michelia crassipes via Regulation of Flavonoid Biosynthesis

WRKY transcription factor (TF) plays a crucial role in plant abiotic stress response, but it is rarely reported in <i>Michelia crassipes</i>. Our studies have found that the transcription factor <i>McWRKY43</i>, a member of the IIc subgroup, is strongly upregulated under cold stress. In this study, we cloned the full length of <i>McWRKY43</i> to further investigate the function of <i>McWRKY43</i> in resistance to cold stress and its possible regulatory pathways in <i>M. crassipes</i>. Under cold stress, the seed-germination rate of transgenic tobacco was significantly higher than that of the wild type, and the flavonoid content, antioxidant enzyme activities, and proline content of transgenic tobacco seedlings were significantly increased, which promoted the expression of flavonoid pathway structural genes. In addition, the transient transformation of <i>McWRKY43</i> in the <i>M. crassipes</i> leaves also found the accumulation of flavonoid content and the transcription level of flavonoid structural genes, especially <i>McLDOX</i>, were significantly increased under cold stress. Yeast one-hybrid (Y1H) assay showed that <i>McWRKY43</i> could bind to <i>McLDOX</i> promoter, and the transcription expression of <i>McLDOX</i> was promoted by <i>McWRKY43</i> during cold stress treatment. Overall, our results indicated that <i>McWRKY43</i> is involved in flavonoid biosynthetic pathway to regulate cold stress tolerance of <i>M. crassipes</i>, providing a basis for molecular mechanism of stress resistance in <i>Michelia</i>.