Over-expression in the nucleotide-binding site-leucine rich repeat gene DEPG1 increases susceptibility to bacterial leaf streak disease in transgenic rice plants.

Bacterial leaf streak of rice (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc) is a widely-spread disease in the main rice-producing areas of the world. Investigating the genes that play roles in rice-Xoc interactions helps us to understand the defense signaling pathway in rice. Here we report a differentially expressed protein gene (DEPG1), which regulates susceptibility to BLS. DEPG1 is a nucleotide-binding site (NBS)-leucine rich repeat (LRR) gene, and the deduced protein sequence of DEPG1 has approximately 64% identity with that of the disease resistance gene Pi37. Phylogenetic analysis of DEPG1 and the 18 characterized NBS-LRR genes revealed that DEPG1 is more closely related to Pi37. DEPG1 protein is located to the cytoplasm, which was confirmed by transient expression of DEPG1-GFP (green fluorescent protein) fusion construct in onion epidermal cells. Semi-quantitative PCR assays showed that DEPG1 is widely expressed in rice, and is preferentially expressed in internodes, leaf blades, leaf sheaths and flag leaves. Observation of cross sections of leaves from the transgenic plants with a DEPG1-promoter::glucuronidase (GUS) fusion gene revealed that DEPG1 is also highly expressed in mesophyll tissues where Xoc mainly colonizes. Additionally, Xoc negatively regulates expression of DEPG1 at the early stage of the pathogen infection, and so do the three defense-signal compounds including salicylic acid (SA), methyl jasmonate (MeJA) and 1-aminocyclopropane-1-carboxylic-acid (ACC). Transgenic rice plants overexpressing DEPG1 exhibit enhanced susceptibility to Xoc compared to the wild-type controls. Moreover, enhanced susceptibility to Xoc may be mediated by inhibition of the expression of some SA biosynthesis-related genes and pathogenesis-related genes that may contribute to the disease resistance. Taken together, DEPG1 plays roles in the interactions between rice and BLS pathogen Xoc.