Homo- and Hetero-Dimers of CAD Enzymes Regulate Lignification and Abiotic Stress Response in Moso Bamboo.

Lignin biosynthesis enzymes form complexes for metabolic channelling during lignification and these enzymes also play an essential role in biotic and abiotic stress response. Cinnamyl alcohol dehydrogenase (CAD) is a vital enzyme that catalyses the reduction of aldehydes to alcohols, which is the final step in the lignin biosynthesis pathway. In the present study, we identified 49 CAD enzymes in five Bambusoideae species and analysed their phylogenetic relationships and conserved domains. Expression analysis of Moso bamboo genes in several developmental tissues and stages revealed that among the genes, has the highest expression level and is expressed in many tissues and , , and were also expressed in most of the tissues studied. Co-expression analysis identified that the positively correlates with most lignin biosynthesis enzymes, indicating that might be the key enzyme involved in lignin biosynthesis. Further, more than 35% of the co-expressed genes with were involved in biotic or abiotic stress responses. Abiotic stress transcriptomic data (SA, ABA, drought, and salt) analysis identified that , and genes were highly upregulated, confirming their involvement in abiotic stress response. Through yeast two-hybrid analysis, we found that , and form homo-dimers. Interestingly, BiFC and pull-down experiments identified that these enzymes form both homo- and hetero- dimers. These data suggest that genes are involved in abiotic stress response and might be a key lignin biosynthesis pathway enzyme. Moreover, this is the first report to show that three PheCAD enzymes form complexes and that the formation of PheCAD homo- and hetero- dimers might be tissue specific.