Systematic Analysis of the Maize CAD Gene Family and Identification of an Elite Drought-Tolerant Haplotype of ZmCAD6

Drought and salt stresses are major abiotic factors limiting maize yield. Lignin, a key cell wall component, plays a crucial role in boosting plant stress resistance. Cinnamyl alcohol dehydrogenase (CAD) is a vital enzyme at the late stage of lignin biosynthesis; however, a systematic study of its functions in abiotic stress responses and its potential for genetic improvement in maize remains lacking. In this study, we conducted the first comprehensive, multi-dimensional analysis of the maize <i>ZmCAD</i> gene family, including gene identification, evolutionary relationships, protein interaction networks, and stress-responsive expression patterns. We identified 9 <i>ZmCAD</i> members that showed significant functional divergence in evolution, structure, and expression patterns. Expression analysis revealed complex, tissue-specific responses of <i>ZmCAD</i> genes to drought and salt stress, with <i>ZmCAD6</i> strongly induced by drought. Importantly, through haplotype analysis of 157 waxy maize inbred lines, we successfully identified an elite haplotype (H3) of <i>ZmCAD6</i> that is significantly associated with improved drought tolerance in maize. This study not only clarifies the functional differentiation mechanisms of the <i>ZmCAD</i> gene family but also provides the identified elite <i>ZmCAD6-H3</i> haplotype as a valuable genetic resource and precise target for molecular breeding aimed at enhancing drought tolerance in maize.