Cloning of the OAT gene and the correlation between its expression and drought tolerance in Phaseolus vulgaris L.

Drought stress is a major abiotic stress of common bean（Phaseolus vulgaris L.） throughout the world. Increasing the proline accumulation contributes to enhance crop drought tolerance. A c DNA for δ-o rnithine aminotransferase（δ-OAT）, an enzyme involved in the biosynthesis of proline, was isolated from Phaseolus vulgaris（Pv OAT）. Pv OAT exhibits 87.4 and 39.8% similarity of the deduced amino acid sequences with δ-OAT from Glycine max and Vigna aconitifolia, respectively. The transcriptional analysis revealed that Pv OAT was strongly induced by drought stress. And the expression of Pv OAT was higher in leaves than that in the root and stem of common bean by drought stress. Similar increase of the proline accumulation was observed in leaves and roots of common bean by drought stress. Furthermore, the proline content, the Pv OAT expression and the Pv OAT enzyme activity in cul tivar F5575 was significantly（P〈0.01） higher than that in cultivar F4851 under drought-stress conditions. Interestingly, it had been observed that, in the later stage of drought stress, the proline steadily maintained at the maximum level maybe result from the Pv OAT enzyme activity increasing steadily. These r esults indicated that the expression of Pv OAT and the accumulation of proline induced by drought stress treatment were related to the degree of common bean drought tolerance. So our results support the view that δ-OAT is associated with proline synthesis under drought stress conditions.

Arbuscular mycorrhizal fungi and endophytic fungi differentially modulate polyamines or proline of peach in response to soil flooding

Symbiotic fungi are involved in plant flooding tolerance,while the underlying mechanism is not yet known.Since polyamines(PAs)and proline are also associated with stress tolerance,it is hypothesized that the enhancement of stress resistance by symbiotic fungi is associated with changes in PAs and/or proline.The aim of this study was to analyze the effect of inoculation with Funneliformis mosseae and Serendipita indica on plant growth,PAs,and proline and the metabolisms in peach(Prunus persica)under flooding.Two-week flooding did not affect root colonization frequence of F.mosseae,while it promoted root colonization frequence of S.indica.Under flooding,plants inoculated with F.mosseae and S.indica maintained relatively higher growth rates than uninoculated plants.Funneliformis mosseae promoted root ornithine(Orn)contentration and arginine(Arg)and Orn decarboxylase activities under flooding,which promoted putrescine(Put),cadaverine(Cad),and spermidine(Spd)contentrations.Conversely,S.indica decreased contentrations of Arg,Orn,and agmatine and Arg decarboxylase activities,thus decreasing PA contentrations under flooding.Polyamines were negatively correlated with the expression of PA uptake transporter genes,PpPUT1 and PpPUT2,in peach.Polyamine transporter genes of F.mosseae(FmTPO)and S.indica(SiTPO)were regulated by flooding,of which FmTPO1 was positively correlated with Put,Cad,and Spd,along with positive correlations of Spd with SiTPO1,SiTPO2,and SiTPO4.Under flooding,F.mosseae decreased proline concentration,while S.indica increased proline concentration and correlated with expression of a△^(1)-pyrroline-5-carboxylate synthetase gene,PpP5CS2.It was thus concluded that F.mosseae modulated polyamine accumulation,while S.indica induced proline accumulation to tolerate flooding.