Spotted-leaf mutants are important to reveal programmed cell death and defense-related pathways in rice. We previously characterized the phenotype performance of a rice spotted-leaf mutant spl21 and narrowed down the causal gene locus spl21(t) to an 87-kb region in chromosome 12 by map-based cloning.
We showed that a single base substitution from A to G at position 836 in the coding sequence of Oryza sativa beta-1,6-N-acetylglucosaminyl transferase (OsGCNT), effectively mutating Tyr to Cys at position 279 in the translated protein sequence, was responsible for the spotted-leaf phenotype as it could be rescued by functional complementation. Compared to the wild type IR64, the spotted-leaf mutant spl21 exhibited loss of chlorophyll, breakdown of chloroplasts, down-regulation of photosynthesis-related genes, and up-regulation of senescence associated genes, which indicated that OsGCNT regulates premature leaf senescence. Moreover, the enhanced resistance to the bacterial leaf blight pathogen Xanthomonas oryzae pv. oryzae, up-regulation of pathogenesis-related genes and increased level of jasmonate which suggested that OsGCNT is a negative regulator of defense response in rice. OsGCNT was expressed constitutively in the leaves, sheaths, stems, roots, and panicles, and OsGCNT-GFP was localized to the Golgi apparatus. High throughput RNA sequencing analysis provided further evidence for the biological effects of loss of OsGCNT function on cell death, premature leaf senescence and enhanced disease resistance in rice. Thus, we demonstrated that the novel OsGCNT regulated rice innate immunity and immunity-associated leaf senescence probably by changing the jasmonate metabolic pathway.
These results reveal that a novel gene Oryza sativa beta-1,6-N-acetylglucosaminyl transferase (OsGCNT) is responsible for the spotted-leaf mutant spl21, and OsGCNT acts as a negative-regulator mediating defense response and immunity-associated premature leaf senescence probably by activating jasmonate signaling pathway.