UGT74B5-Mediated Glucosylation at ortho Hydroxyl Groups of Benzoic Acid Derivatives Regulating Plant Immunity to Anthracnose in Tea Plants

Abstract

Benzoates, particularly salicylic acid (SA) and its derivatives, play critical roles in plant immune responses and basal defense through hydroxylation and glycosylation. Anthracnose is one of the most common and devastating diseases in tea plants (Camellia sinensis). However, the role of SA and its derivatives in tea plant immunity and resistance to anthracnose remains largely unexplored. In present study, we identified and characterized a glycosyltransferase, CsUGT74B5, which was significantly downregulated in tea seedlings upon anthracnose infection. CsUGT74B5 was preferentially expressed in mature leaves and stem, and responded rapidly to exogenous SA treatment. Phylogenetic analysis suggested CsUGT74B5 might possess the catalytic activity toward benzoates. Enzymatic assays and molecular docking demonstrated recombinant CsUGT74B5 specifically glycosylated at the ortho hydroxyl groups of SA and 2, 6-dihydroxybenzoic acid (2, 6-DHBA), but did not glycosylate 2, 3-DHBA, 2, 5-DHBA or other substrates in vitro. Overexpression of CsUGT74B5 in Arabidopsis thaliana and tobacco (Nicotiana tabacum) reduced SA level while promoting the accumulation of SA 2-O-β-D-glucoside (SAG), further validating the in vivo function of CsUGT74B5. Moreover, transient overexpression of CsUGT74B5 in two tea plant cultivars increased their sensitivity to anthracnose and accelerated lesion development, which was attributed to decreased SA levels. Overall, our finding demonstrated that CsUGT74B5-mediated biosynthesis of SAG regulated tea plant immunity against anthracnose by fine-tuning free SA levels, providing new progress into the immunity response of tea plants.