Ectopic Expression of Glycine max GmNAC109 Enhances Drought Tolerance and ABA Sensitivity in Arabidopsis

Abstract

The NAC (NAM, ATAF1/2, CUC2) transcription factors are widely known for their various functions in plant development and stress tolerance. Previous studies have demonstrated that genetic engineering can be applied to enhance drought tolerance via overexpression/ectopic expression of NAC genes. In the present study, the dehydration- and drought-inducible GmNAC109 from Glycine max was ectopically expressed in Arabidopsis (GmNAC109-EX) plants to study its biological functions in mediating plant adaptation to water deficit conditions. Results revealed an improved drought tolerance in the transgenic plants, which displayed greater recovery rates by 20% to 54% than did the wild-type plants. In support of this finding, GmNAC109-EX plants exhibited lower water loss rates and decreased endogenous hydrogen peroxide production in leaf tissues under drought, as well as higher sensitivity to exogenous abscisic acid (ABA) treatment at germination and early seedling development stages. In addition, analyses of antioxidant enzymes indicated that GmNAC109-EX plants possessed stronger activities of superoxide dismutase and catalase under drought stress. These results together demonstrated that GmNAC109 acts as a positive transcriptional regulator in the ABA-signaling pathway, enabling plants to cope with adverse water deficit conditions.

The Soybean GmNAC019 Transcription Factor Mediates Drought Tolerance in Arabidopsis in an Abscisic Acid-Dependent Manner

“…When compared with WT plants, all three transgenic lines were smaller in size, as indicated by examination of several phenotypic parameters, including rosette radius and area, and root length ( Figure 1B,C). These findings imply that constitutive expression of NAC genes using the CaMV 35S promoter might result in growth retardation in homologous/heterologous transgenic systems, as also observed in many previously published reports, such as ectopic expression of GmNAC085 [69] or GmNAC109 [70] in Arabidopsis, and overexpression of Thellungiella halophila TsNAC1 in T. halophila [71] or ANAC036 in Arabidopsis [72]. Additional analyses from some of these studies reveal that the restriction in cell size and expansion was a cause of growth retardation, probably due to the strong activity of this promoter [71,72].…”

“…In all experiments performed in this study, the seeds were surface-sterilized prior to germination. The information for seed sterilization, germination and growing condition was described in a previously published study [70]. When the plants were transferred to soil for an assay, the relative soil moisture contents (SMCs) were regularly monitored, with the aid of a Moisture Meter (TK-100G, Yieryi, Guangdong, China), by measuring spontaneously six different positions per time point to obtain the average SMC values.…”

“…Survival rate upon drought exposure was determined following the same-tray method in which the wild-type (WT) and transgenic plants were grown on the same trays [70]. In brief, two-week-old seedlings were transferred from MS plates to soil.…”

“…Four-week-old plants of all genotypes were subjected to a water withholding treatment for 12 days before the leaf tissues (0.2 g per plant for each replicate, three replicates per genotype) were collected for measurement. H 2 O 2 content was determined following the previous method [99] with minor modifications according to Nguyen et al [70]. For enzymatic activity analyses, 0.2 g leaves were ground in 2 mL of pre-chilled extraction buffer (potassium phosphate buffer 1 M, EDTA 0.1 M and 2% polyvinylpyrrolidone (molecular weight 8000), pH 7.8).…”

“…A preparation similar to the germination assay was also performed for examining the effect of ABA on cotyledon greening after seven days of incubation, by calculating the proportion of seedlings displaying green cotyledon [106]. The plates were kept under non-stressed growth conditions [70]. For each assay, three sets of replicates of each genotype, with the size of 100 seeds per replicate, were analyzed.…”