Rice Snl6, a Cinnamoyl-CoA Reductase-Like Gene Family Member, Is Required for NH1-Mediated Immunity to Xanthomonas oryzae pv. oryzae

Abstract

Rice NH1 (NPR1 homolog 1) is a key mediator of innate immunity. In both plants and animals, the innate immune response is often accompanied by rapid cell death at the site of pathogen infection. Over-expression of NH1 in rice results in resistance to the bacterial pathogen, Xanthomonas oryzae pv. oryzae (Xoo), constitutive expression of defense related genes and enhanced benzothiadiazole (BTH)- mediated cell death. Here we describe a forward genetic screen that identified a suppressor of NH1-mediated lesion formation and resistance, snl6. Comparative genome hybridization and fine mapping rapidly identified the genomic location of the Snl6 gene. Snl6 is a member of the cinnamoyl-CoA reductase (CCR)-like gene family. We show that Snl6 is required for NH1-mediated resistance to Xoo. Further, we show that Snl6 is required for pathogenesis-related gene expression. In contrast to previously described CCR family members, disruption of Snl6 does not result in an obvious morphologic phenotype. Snl6 mutants have reduced lignin content and increased sugar extractability, an important trait for the production of cellulosic biofuels. These results suggest the existence of a conserved group of CCR-like genes involved in the defense response, and with the potential to alter lignin content without affecting development. Plants possess potent and effective endogenous methods for responding to pathogen attacks, referred to as plant innate immunity. In this report we further our understanding of rice innate immunity through characterization of the Snl6 gene. The snl6 mutant was identified from a mutant screen for positive regulators of immunity. While innate immunity represents a powerful agronomic tool, identification of desirable genes from crop species is limited by the slow and laborious nature of map-based cloning. Here we describe our methodology of combining comparative genome hybridization and fine mapping to rapidly identify the Snl6 gene. Snl6 is distantly related to members of the cinnamoyl-CoA reductase gene family, is required for pathogenesis gene expression and resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae. Snl6 mutants have reduced lignin content and increased sugar extractability, an important trait for the production of cellulosic biofuels.