Overexpression of Rhizobium rhizogenes A4-rolB enhances osmotic stress resistance in Arabidopsis.

BACKGROUND: Functional investigation of individual Rhizobium rhizogenes oncogene contributes to a deeper understanding of the mechanisms underlying R. rhizogenes-plant transformation, which holds the potential of enhancing plants' abiotic stress resistance. The root oncogenic locus (rol) B gene, a key oncogene of R. rhizogenes, was reported to participate in abiotic stress resistance in transformed plants. Yet, the underlying mechanisms remain largely elusive. This study investigated Arabidopsis overexpressing A4-rolB (rolB-OX) for phenotypic modifications and short-term osmotic stress resistance. RESULTS: Data showed that A4-rolB induced pronounced dwarfing phenotypes and weakened root growth in rolB-OX as shown by its compact growth and significantly decreased root length and root surface area (59% and 63% of wild type Col-0, respectively) under normal growth conditions. Under polyethylene glycol 6000 (PEG) 10% (w/v)-induced osmotic stress, rolB-OX exhibited enhanced resistance to osmotic stress compared with Col-0, as exemplified by less severe leaf wilting, increased total antioxidant capacity (TAC), and a better recovery of stomatal conductance after PEG treatment. Moreover, A4-rolB mediated enhancement in abscisic acid (ABA) levels under well-watered conditions, which may have facilitated stress resistance of rolB-OX under PEG exposure, probably through inducing TAC. Furthermore, after PEG stress, rolB-OX exhibited dramatically up-regulated (3.3-5.7-fold of Col-0) transcript levels of genes encoding plasma membrane intrinsic proteins (PIPs) (i.e., PIP2;5 and PIP2;7), which are correlated with an improved plant hydraulic conductivity. CONCLUSIONS: This study reports an enhanced osmotic stress resistance in rolB-OX, which could be attributed to A4-rolB-mediated increase in leaf ABA levels and TAC and improved stomatal regulation. Furthermore, the association between ABA and TAC, and its effect on the osmotic stress resistance caused by rolB, was thoroughly discussed in this study. These findings reveal novel physiological effects of A4-rolB on plant abiotic stress resistance.