Genome-Wide Identification of Laccases Reveals Potential Targets for Lignin Modification.

Laccase is a key enzyme in plant lignin biosynthesis as it catalyzes the final step of monolignols polymerization. Sweet sorghum [ (L.) Moench] is considered as an ideal feedstock for ethanol production, but lignin greatly limits the production efficiency. No comprehensive analysis on laccase has ever been conducted in , although it appears as the most promising target for engineering lignocellulosic feedstock. The aim of our work is to systematically characterize laccase gene family and to identify the lignin-specific candidates. A total of twenty-seven laccase candidates (-) were identified in . All SbLACs comprised the equivalent L1-L4 signature sequences and three typical Cu-oxidase domains, but exhibited diverse intron-exon patterns and relatively low sequence identity. They were divided into six groups by phylogenetic clustering, revealing potential distinct functions, while SbLAC5 was considered as the closest lignin-specific candidate. qRT-PCR analysis deciphered that genes were expressed preferentially in roots and young internodes of sweet sorghum, and showed high expression, adding the evidence that was involved in lignin biosynthesis. Besides, high abundance of transcripts was detected, correlating it a potential role in lignin biosynthesis. Diverse regulatory elements were recognized in promoters, indicating putative interaction with transcription factors. Seven were found to be potential targets of sbi-miRNAs. Moreover, putative phosphorylation sites in SbLAC sequences were identified. Our research adds to the knowledge for lignin profile modification in sweet sorghum.