Abstract
Sugarcane (Saccharum spp.), a vital economic crop, suffers significant yield losses from drought. This study elucidates the genetic regulation of lignin biosynthesis-a key drought-resistance mechanism-by analyzing three contrasting accessions: drought-sensitive Saccharum officinarum (Badila), drought-resistant hybrid (XTT22), and drought-tolerant wild Saccharum spontaneum (SES-208) under progressive drought (7-21 days). Physiological analyses revealed pronounced lignin accumulation in XTT22 roots/leaves, driven by elevated coniferyl/sinapyl alcohol substrates, while Badila showed minimal deposition. Genomic characterization of cinnamyl/sinapyl alcohol dehydrogenase (CAD/SAD) families across six sugarcane genomes identified 322 genes phylogenetically clustered into three clades. Class I members (CAD1, CAD5, etc.) were critical for lignin biosynthesis, with tandem/segmental duplications driving family expansion and promoters enriched in stress-responsive cis-elements (ABA, MeJA, light). Transcriptomics and qRT-PCR confirmed strong correlations between Class I CAD expression, lignin content, and drought tolerance. These findings establish CAD Class I genes as novel molecular targets for enhancing drought resilience in sugarcane breeding programs.