Mutation of the chitinase-like protein-encoding AtCTL2 gene enhances lignin accumulation in dark-grown Arabidopsis seedlings

Several genes that encode a chitinase-like protein (called the CTL group) have been identified in Arabidopsis, rice, pea, and cotton. Members of the CTL group have attracted much attention because of their possible role in the biosynthesis of the cell wall in plants. The hot2 mutation in the CTL1 (AtCTL1) gene of Arabidopsis thaliana causes multiple defects in growth and development. The Arabidopsis genome possesses the AtCTL2 gene, which exhibits 70% similarity to AtCTL1 at the amino acid level. We showed that the AtCTL2 gene was predominantly expressed in stems, which was in contrast to the presence of AtCTL1 transcripts in most organs of Arabidopsis. In addition, β-glucuronidase (GUS) staining was detectable in all tissues of the stem in transgenic plants expressing the AtCTL1::GUS construct, while GUS activity under control of the AtCTL2 promoter was significantly restricted to the xylem and to interfascicular fibers in stems. The phenotypes of atctl2 single mutant and of hot2, atctl2 double mutant plants were significantly similar to those of wild-type and of hot2 single mutant plants, respectively. The expression levels of CESA1 and CESA4 transcripts were not affected in the two single mutants or corresponding double mutant plants, compared with the levels in wild-type plants. The accumulation of lignin in etiolated hypocotyls, however, was increased by mutation of AtCTL2. These findings suggest that AtCTL2 is required for proper cell wall biosynthesis in etiolated seedlings of Arabidopsis.