Identification of a cluster of PR4-like genes involved in stress responses in rice

PR4 proteins constitute a pathogenesis-related (PR) protein family with a conserved BARWIN domain. In this study, we analyzed PR4-homologous genes in rice (Oryza sativa L.) and identified five putative PR4 genes designated as OsPR4a-e. The five PR4 genes are located in tandem on chromosome 11 and constitute a gene cluster with high sequence similarity to each other. The OsPR4 proteins have high sequence similarity to reported PR4 proteins from monocotyledonous species and are predicted to be class II PR4 proteins. Distinct diversification of plant PR4 proteins exists between monocotyledonous and dicotyledonous plants. Except for OsPR4e, which was not detected with any transcript, the other four OsPR4 genes showed diverse temporal-spatial expression patterns, and their expressions are responsive to Magnaporthe grisea infection. Interestingly, the OsPR4 genes are also responsive to abiotic stresses. Their expression levels were strongly induced by at least one of the stress treatments including drought, salt, cold, wounding, heat shock, and ultraviolet. The transcript levels of OsPR4 genes were also induced by some phytohormones such as abscisic acid and jasmonic acid. Transgenic rice with overexpression of OsPR4a showed enhanced tolerance to drought at both seedling and reproductive stages. We conclude that rice PR4 genes are also involved in abiotic stress responses and tolerance in addition to their responsiveness to pathogen attacks.