Genome-wide identification and characterization of laccase gene family in Citrus sinensis

In plants, the final step of monolignols polymerization is catalyzed by laccase, a key enzyme in lignin biosynthesis. Laccase has been shown a multifunctional enzyme that plays many important roles. As information is not available on the laccase gene family in Citrus sinensis, genome-wide analysis has been carried out in this study using C. sinensis genome. Using bioinformatics approaches, 24 laccase genes (CsLAC1~CsLAC24) were identified from C. sinensis. Most CsLACs were found in C. sinensis chromosome 6, 7 and 8, while no CsLACs were found in chromosome 4, 5 and 9. In most CsLACs, four conserved signature sequences and three typical Cu-oxidase domains were observed. However, the CsLAC-encoding genes displayed distinct intron-exon patterns and relatively low sequence similarity. Phylogenetic clustering analysis indicated that the CsLACs were divided into seven groups, suggesting potential distinct functions and evolution. Putative signal sequences, subcellular location and glycosylation sites were predicted in the CsLACs. Moreover, sixteen CsLAC transcripts, which coding genes were clustering in chromosomes, were found to be potential targets of csi-miR397. Cis-regulatory elements and expression analyses indicated the possible involvement of some CsLAC members in diverse stresses and growth/development processes, respectively. These results may provide valuable clues for further studies on the functions of the CsLACs in citrus growth and adaptation to stress.