Title : Acetylcholine induces down regulation in GmABA2 and GmLEA3 in soybean plants under water deficit
Water deficiency is a particularly limiting factor for the development and production of diverse crops, which can have a significantly detrimental impact on agriculture. Some bioregulators can be used as priming to minimize the damaging effects of water stress. Bioregulators, such as Acetylcholine (Ach) act in the regulation of the stomatal movement and being considered as ABA antagonist, respectively. This is because the enzyme encoding the GmABA2 gene catalyzes the conversion of xanthoxine to abscisic aldehyde, the latter being converted to ABA, the expression of the GmABA2 gene can also be used as an indicator for studies on soybean drought responses. LEA genes are induced by ABA or through environmental stress, such as water deficiency. It is suggested that such proteins act on water retention in ion sequestration and have the ability to stabilize membranes and proteins. The objective of this study was to analyze different modes of exogenous application of Ach and to study its effect on the regulation of the relative transcriptional responses of the GmABA2 and GmLEA3 genes in soybean, induced by water deficit using RTqPCR. For this we used an application of Ach in the concentration of 2.0 mM in soybean plants cv. Intact under different water regimes. The factors studied were: 1) the application of bioregulators (i) in seeds- S (ii) in leaf -L ; (iii) in the seed and leaf - SL; (iv) control without application - C; and (2) water regimes: (i) 100% of field capacity (FC) and (ii) irrigation suspension (IS). The GmABA2 gene, for the treatments that were under water deficit, for the control treatment, when the bioregulators were not applied, its expression was 3.6 times higher (Log2 = 3.59), in relation to the control with 100% of field capacity. A low transcriptional level of this gene was observed for all treatments with Ach (S, SL and L), Log2 = 1.6, 0.8 and 1.8 fold in change, relative to the control treatment. The GmLEA3 gene exhibited a higher number of transcripts in the treatments under water deficit for the control treatment, without application of Ach, compared to the other treatments, presenting a value of Log2 = 5.9, an increase of approximately 5 times in the number of transcripts compared to treatment with 100% of field capacity. Regarding the application of Ach, it was observed that the treatments with leaf applications (SL and L) showed a down regulation of the gene expression, Log2 = 1.7 and 2.6, compared to the control under water deficit (Log2 = 5.9). The application of Ach in seed and leaf showed a down regulation of GmABA2 and GmLEA3 genes. In addition, LEA proteins are accumulated in plant tissues exposed to water deficiency, osmotic stress at high temperature in soybean and, thus, may indicate the level of stress present in plants treated and untreated with Ach. The difference in the transcriptional level of GmABA2 with and without Ach, in soybean plants under water deficit, suggests that in the present study, Ach played a role in the regulation of signaling, reducing the signaling and activation of genes responsible for ABA biosynthesis.