Mechanism of the drought tolerance of a transgenic soybean overexpressing the molecular chaperone BiP

Abstract

Drought is one of major constraints that limits agricultural productivity. Some factors, including climate changes and acreage expansion, indicates towards the need for developing drought tolerant genotypes. In addition to its protective role against endoplasmic reticulum (ER) stress, we have previously shown that the molecular chaperone binding protein (BiP) is involved in the response to osmotic stress and promotes drought tolerance. Here, we analyzed the proteomic and metabolic profiles of BiP-overexpressing transgenic soybean plants and the corresponding untransformed line under drought conditions by 2DE-MS and GC/ MS. The transgenic plant showed lower levels of the abscisic acid and jasmonic acid as compared to untransformed plants both in irrigated and non-irrigated conditions. In contrast, the level of salicylic acid was higher in transgenic lines than in untransformed line, which was consistent with the antagonistic responses mediated by these phytohormones. The transgenic plants displayed a higher abundance of photosynthesis-related proteins, which gave credence to the hypothesis that these transgenic plants could survive under drought conditions due to their genetic modification and altered physiology. The proteins involved in pathways related to respiration, glycolysis and oxidative stress were not signifcantly changed in transgenic plants as compared to untransformed genotype, which indicate a lower metabolic perturbation under drought of the engineered genotype. The transgenic plants may have adopted a mechanism of drought tolerance by accumulating osmotically active solutes in the cell. As evidenced by the metabolic profiles, the accumulation of nine primary amino acids by protein degradation maintained the cellular turgor in the transgenic genotype under drought conditions. Thus, this mechanism of protection may cause the physiological activities including photosynthesis to be active under drought conditions.

A Regulatory Circuit Integrating Stress-Induced with Natural Leaf Senescence

“…The BiP-mediated tolerance mechanism is not associated with conventional mechanisms of drought tolerance and avoidance, as the BiPoverexpressing lines do not display lower photosynthesis and transpiration rates than untransformed lines under drought, and the stomata closure and root growth are not stimulated under water deprivation. Furthermore, the BiP-overexpressing lines exhibit a lower induction of drought-related genes than WT under waterdeficit conditions, and the abscisic acid content in BiP-overexpressing plants is similar to untransformed lines, indicating that the BiP-mediated drought tolerance mechanism is independent on ABA [59,64,65]. Under drought conditions, the only variations observed in BiP-overexpressing lines are a delay in drought-induced leaf senescence and an attenuation in the drought induction of PCD-associated marker genes, which is associated with the protective function of BiP as a negative modulator of the DCD/NRP-mediated cell death response.…”

“…Due to a higher osmolyte accumulation, mainly amino acids, the BiP-overexpressing plants can maintain the leaf turgidity upon drought stress, which is a phenotypic hallmark of the BiP-mediated tolerance to drought. The BiPoverexpressing lines also display a higher accumulation of salicylic acid and upregulation of SA-responsive genes, which is associated with accelerated hypersensitive response triggered by Pseudomonas syringae pv tomato in soybean and tobacco [59,65]. The SA signaling also activates the antioxidative metabolism, which may be linked to the BiP protective function to drought.…”

“…Under drought conditions, the only variations observed in BiP-overexpressing lines are a delay in drought-induced leaf senescence and an attenuation in the drought induction of PCD-associated marker genes, which is associated with the protective function of BiP as a negative modulator of the DCD/NRP-mediated cell death response. A metabolomic approach was used to detect the metabolite profile of BiP-overexpressing lines under drought conditions [65]. Due to a higher osmolyte accumulation, mainly amino acids, the BiP-overexpressing plants can maintain the leaf turgidity upon drought stress, which is a phenotypic hallmark of the BiP-mediated tolerance to drought.…”

Proteomic and Metabolomic Analysis of a Drought Tolerant Soybean Cultivar from Brazilian Savanna

“…The isoelectric focusing (IEF) was performed in a 13 cm IPG strip pH 3-10 (GE Healthcare, Chicago, USA) as described by Coutinho [21]…”

“…Ten milligrams of powdered tissue (~110 mg fresh weight) was mixed with 400 μL of methanol, isopropanol and acetic acid (20:79:1). The phytohormones were extracted and analyzed as described by Coutinho [21]. The sample was scanned by MRM (multiple reaction monitoring) to detect each hormone as shown in Supplementary Table S1.…”