Comparative hormonal regulatory pathway of the drought responses in relation to glutamate-mediated proline metabolism in Brassica napus

Proline metabolism influences metabolic and signaling pathway in regulating plant stress responses. This study aimed to characterize the physiological significance of glutamate (Glu)-mediated proline metabolism in the drought stress responses, focusing on the hormonal regulatory pathway. The responses of cytosolic Ca2+ signaling, proline metabolism and redox components to the exogenous application of Glu in well-watered or drought-stressed plants were interpreted in relation to endogenous hormone status and their signaling genes. Drought-enhanced abscisic acid (ABA) were concomitant with ROS and proline accumulation, accompanied by decreased NAD(P)H/NAD(P)+ and GSH/GSSG ratios. Exogenous Glu-feeding under drought resulted in an increase of salicylic acid (SA) with an antagonistic decrease of ABA. Glu-enhanced SA coincided with the highest expression of SA synthesis related gene ICS1 and Ca2+-dependent protein kinase CPK5. SA-enhanced CPK5 expression was closely associated with further enhancement of proline synthesis-related genes (P5CS1, P5CS2, and P5CR) expression. The Glu-activated proline synthesis was responsible for the reset of reducing potential with enhanced expression of redox regulating genes TRXh5 and GRXC9 in a SA-mediated NPR1- and/or PR1-dependent manner. These results clearly indicate that Glu-activated interplay between SA- and CPK5-signaling and Glu-enhanced proline synthesis are crucial in the amelioration of drought stress in B. napus.\n\nHighlightO_LIDrought-induced oxidative stress and symptom are developed by ABA-dependent manner\nC_LIO_LIGlu-application increases endogenous SA level with an antagonistic decrease of ABA\nC_LIO_LIDrought-induced proline accumulation was further enhanced by exogenous Glu-application\nC_LIO_LIGlu-enhanced proline synthesis accompanied with SA-mediated regulatory pathway\nC_LIO_LIGlu-enhanced SA-modulated proline metabolism is an integrated process of redox control\nC_LI