Systemic acquired resistance in soybean is regulated by two proteins, Orthologous to Arabidopsis NPR1.

BACKGROUND: Systemic acquired resistance (SAR) is induced in non-inoculated leaves following infection with certain pathogenic strains. SAR is effective against many pathogens. Salicylic acid (SA) is a signaling molecule of the SAR pathway. The development of SAR is associated with the induction of pathogenesis related (PR) genes. Arabidopsis non-expressor of PR1 (NPR1) is a regulatory gene of the SA signal pathway 123. SAR in soybean was first reported following infection with Colletotrichum trancatum that causes anthracnose disease. We investigated if SAR in soybean is regulated by a pathway, similar to the one characterized in Arabidopsis. RESULTS: Pathogenesis-related gene GmPR1 is induced following treatment of soybean plants with the SAR inducer, 2,6-dichloroisonicotinic acid (INA) or infection with the oomycete pathogen, Phytophthora sojae. In P. sojae-infected plants, SAR was induced against the bacterial pathogen, Pseudomonas syringae pv. glycinea. Soybean GmNPR1-1 and GmNPR1-2 genes showed high identities to Arabidopsis NPR1. They showed similar expression patterns among the organs, studied in this investigation. GmNPR1-1 and GmNPR1-2 are the only soybean homologues of NPR1and are located in homoeologous regions. In GmNPR1-1 and GmNPR1-2 transformed Arabidopsis npr1-1 mutant plants, SAR markers: (i) PR-1 was induced following INA treatment and (ii) BGL2 following infection with Pseudomonas syringae pv. tomato (Pst), and SAR was induced following Pst infection. Of the five cysteine residues, Cys82, Cys150, Cys155, Cys160, and Cys216 involved in oligomer-monomer transition in NPR1, Cys216 in GmNPR1-1 and GmNPR1-2 proteins was substituted to Ser and Leu, respectively. CONCLUSION: Complementation analyses in Arabidopsis npr1-1 mutants revealed that homoeologous GmNPR1-1 and GmNPR1-2 genes are orthologous to Arabidopsis NPR1. Therefore, SAR pathway in soybean is most likely regulated by GmNPR1 genes. Substitution of Cys216 residue, essential for oligomer-monomer transition of Arabidopsis NPR1, with Ser and Leu residues in GmNPR1-1 and GmNPR1-2, respectively, suggested that there may be differences between the regulatory mechanisms of GmNPR1 and Arabidopsis NPR proteins.

Expression and evolution of the phosphoinositide-specific phospholipase C gene family in Arabidopsis thaliana.

Phosphoinositide-specific phospholipase C cleaves the substrate phosphatidylinositol 4,5-bisphosphate and generates inositol 1,4,5-trisphosphate and 1,2-diacylglycerol, both of which are second messengers in the phosphoinositide signal transduction pathways operative in animal cells. Five PI-PLC isoforms, beta, gamma, delta, epsilon and zeta, have been identified in mammals. Plant PI-PLCs are structurally close to the mammalian PI-PLC-zeta isoform. The Arabidopsis genome contains nine AtPLC genes. Expression patterns of all nine genes in different organs and in response to various environmental stimuli were studied by applying a quantitative RT-PCR approach. Multiple members of the gene family were differentially expressed in Arabidopsis organs, suggesting putative roles for this enzyme in plant development, including tissue and organ differentiation. This study also shows that a majority of the AtPLC genes are induced in response to various environmental stimuli, including cold, salt, nutrients Murashige-Skoog salts, dehydration, and the plant hormone abscisic acid. Results of this and previous studies strongly suggest that transcriptional activation of the PI-PLC gene family is important for adapting plants to stress environments. Expression patterns and phylogenetic relationships indicates that AtPLC gene members probably evolved through multiple rounds of gene duplication events, with AtPLC4 and AtPLC5 and AtPLC8 and AtPLC9 being duplicated in tandem in recent times.