Differential gene expression of rice roots inoculated with the diazotroph Herbaspirillum seropedicae

Rice (Oryza sativa L.) is the primary source of carbohydrate for the majority of the World's population. Herbaspirillum seropedicae is a diazotroph that lives within and on the surface of rice roots. It can promote the growth of rice, partly by supplying it with fixed nitrogen. To better understand the rice-H. seropedicae interaction, cDNA libraries from rice roots either inoculated (RRCH) or uninoculated (RRSH) with the diazotroph were obtained and analysed. Potential differentially expressed genes identified from the libraries encoded a metallothionein-like protein type 1, a NOD26-like membrane integral protein ZmNIP2-1, a thionin family protein, an oryzain gamma chain precursor, stress-associated protein 1 (OsISAP1), probenazole-inducible protein PBZ1 and auxin- and ethylene-responsive genes. Differential expression was analysed by qRT-PCR for some of these genes and confirmed in most cases. The expression of stress- and defence-related genes coding for thionins, PBZ1 and OsISAP1 was repressed, while expression of a metallothionein gene was induced by inoculation with H. seropedicae. In contrast, expression of auxin-responsive genes was repressed, while expression of ethylene genes was either repressed or induced. The possible involvement of these and other genes in plant-bacterial interactions is discussed. The decrease in expression of the defence-related proteins PBZ1 and thionins in the rice-H. seropedicae association, suggests that the bacteria modulate plant defence responses during colonisation. The expression of genes responsive to auxin and ethylene also appears to be regulated by the bacteria.