Antagonistic functions of CTL1 and SUH1 mediate cell wall assembly in Arabidopsis

Plant genomes contain numerous genes encoding chitinase-like (CTL) proteins, which have a similar protein structure to chitinase but lack the chitinolytic activity to cleave the β-1,4-glycosidic bond in chitins, polymers of N- acetylglucosamine. Mutations in CTL1 in rice and Arabidopsis have been found to cause pleiotropic developmental defects, including altered cell wall composition and decreased abiotic stress tolerance, likely due to a reduction in cellulose content. In this study, we identified suppressor of hot2-1 (suh1) as a genetic suppressor of the ctl1hot2-1 mutation in Arabidopsis. The mutation in SUH1 restored almost all ctl1hot2-1 defects examined to nearly wild-type levels, with the exception of partial recovery of cellulose content in ctl1hot2-1 mutants. SUH1 encodes a Golgi-located type II membrane protein with glycosyltransferase (GT) activity, and its mutations lead to reduction in cellulose content and hypersensitivity to cellulose biosynthesis inhibitors, although to a lesser extent than ctl1hot2-1 mutation. The SUH1 promoter fused with the GUS reporter gene exhibited GUS activity in interfascicular fibers and xylem in stems, and this activity was significantly increased by the ctl1hot2-1 mutation. Our findings provide genetic and molecular evidence that the antagonistic activities of CTL1 and SUH1 play an essential role in cell wall assembly in Arabidopsis.