Ectopic Expression of a Cell-Wall-Degrading Enzyme-Induced OsAP2/ERF152 Leads to Resistance against Bacterial and Fungal Infection in Arabidopsis.

Pathogen secreted cell-wall-degrading enzymes (CWDEs) induce plant innate immune responses. The expression of rice transcription factor APETALA2/ethylene response factor-152 (OsAP2/ERF152) is enhanced in leaves upon treatment with different CWDEs and upon wounding. Ectopic expression of OsAP2/ERF152 in Arabidopsis leads to induction of immune responses such as callose deposition and upregulation of both salicylic acid- and jasmonic acid/ethylene-responsive defense genes. Arabidopsis transgenics expressing OsAP2/ERF152 exhibited resistance to infections caused by both bacterial and fungal pathogens (Pseudomonas syringae pv. tomato DC3000 and Rhizoctonia solani AG1-IA, respectively). Ectopic expression of OsAP2/ERF152 results in transient activation of mitogen-activated protein kinases 3/6 (MPK3/6), which could be leading to the induction of a broad range immunity in Arabidopsis.

Rice Leaf Transcriptional Profiling Suggests a Functional Interplay Between Xanthomonas oryzae pv. oryzae Lipopolysaccharide and Extracellular Polysaccharide in Modulation of Defense Responses During Infection.

Treatment of rice leaves with isolated Xanthomonas oryzae pv. oryzae lipopolysaccharide (LPS) induces the production of callose deposits, reactive oxygen species, and enhanced resistance against subsequent bacterial infection. Expression profiling of X. oryzae pv. oryzae LPS-treated rice (Oryza sativa subsp. indica) leaves showed that genes involved in the biosynthetic pathways for lignins, phenylpropanoids, chorismate, phenylalanine, salicylic acid, and ethylene, as well as a number of pathogenesis-related proteins are up-regulated. Gene ontology categories like cell-wall organization, defense response, stress response, and protein phosphorylation/kinases were found to be upregulated, while genes involved in photosynthesis were down-regulated. Coinfiltration with xanthan gum, the xanthomonas extracellular polysaccharide (EPS), suppressed LPS-induced callose deposition. Gene expression analysis of rice leaves that are treated with an EPS-deficient mutant of X. oryzae pv. oryzae indicated that a number of defense-regulated functions are up-regulated during infection. These transcriptional responses are attenuated in rice leaves treated with an EPS-deficient mutant that is also deficient in the O-antigen component of LPS. Overall, these results suggest that the O-antigen component of X. oryzae pv. oryzae LPS induces rice defense responses during infection and that these are suppressed by bacterial EPS.