ABSTRACT. We evaluated the molecular, anatomical and physiological properties of a soybean line transformed to improve drought tolerance with an rd29A:AtDREB1A construct. This construct expressed dehydrationresponsive element binding protein DREB1A from the stress-inducible rd29A promoter. The greenhouse growth test included four randomized blocks of soybean plants, with each treatment performed in triplicate. Seeds from the non-transformed soybean cultivar BR16 and from the genetically modified soybean P58 line (T 2 generation) were grown at 15% gravimetric humidity for 31 days. To induce water deficit, the humidity was reduced to 5% gravimetric humidity (moderate stress) for 29 days and then to 2.5% gravimetric humidity (severe stress). AtDREB1A gene expression was higher in the genetically modified P58 plants during water deficit, demonstrating transgene stability in T 2 generations and induction of the rd29A promoter. Drought-response genes, including GmPI-PLC, GmSTP, GmGRP, and GmLEA14, were highly expressed in plants submitted to severe stress. Genetically modified plants had higher stomatal conductance and consequently higher photosynthetic and transpiration rates. In addition, they had more chlorophyll. Overexpression of AtDREB1A may contribute to a decrease in leaf thickness; however, a thicker abaxial epidermis was observed. Overexpression of AtDREB1A in soybean appears to enhance drought tolerance.

ABSTRACT. To gain insight into stress-responsive gene regulation in soybean plants, we identified consensus sequences that could categorize the transcription factors MYBJ7, BZIP50, C2H2, and NAC2 as members of the gene families myb, bzip, c2h2, and nac, respectively. We also investigated the evolutionary relationship of these transcription factors and analyzed their expression levels under drought stress. The NCBI software was used to find the predicted amino acid sequences of the transcription factors, and the Clustal X software was used to align soybean and other plant species sequences. Phylogenetic trees were built using the Mega 4.1 software by neighbor joining and the degree of confidence test by Bootstrap. Expression level studies were carried out using hydroponic culture; the experiments were designed in completely randomized blocks with three repetitions. The blocks consisted of two genotypes, MG/ BR46 Conquista (drought-tolerant) and BR16 (drought-sensitive) and the treatments consisted of increasingly long dehydration periods (0, 25, 50, 75, and 100 min). The transcription factors presented domains and/or conserved regions that characterized them as belonging to the bzip, c2h2, myb, and nac families. Based on the phylogenetic trees, it was found that the myb, bzip and nac genes are closely related to myb78, bzip48 and nac2 of soybean and that c2h2 is closely related to c2h2 of Brassica napus. Expression of all genes was in general increased under drought stress in both genotypes.Major differences between genotypes were due to the lowering of the expression of the mybj7 and c2h2 genes in the drought-tolerant variety at some times. Over-expression or silencing of some of these genes has the potential to increase stress tolerance.

The low activity and the competing reactions catalysed by Rubisco are major limitations to photosynthetic carbon assimilation in C3 plants; the present paper considers how these limitations can be overcome. The limitations could be most effectively addressed by introducing Rubisco with a higher catalytic rate and/or better able to discriminate between gaseous substrates. Although enzymes with desirable characteristics are available, technical advances are required before their potential can be realized in major crop plants. Significant improvements could be achieved also by increasing the concentrations of the productive substrates, CO2 and RuBP, at the active site of Rubisco. Critically, it is essential that other environmental and genotype constraints are minimized, to realize the highest photosynthetic potential.

ABSTRACT. Abscisic acid-responsive element binding protein (AREB1) is a basic domain/leucine zipper transcription factor that binds to the abscisic acid (ABA)-responsive element motif in the promoter 6273 ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 13 (3): 6272-6286 (2014) Water deficit response in GM soybeans with AtAREB1∆QT region of ABA-inducible genes. Because AREB1 is not sufficient to direct the expression of downstream genes under non-stress conditions, an activated form of AREB1 (AREB1∆QT) was created. Several reports claim that plants overexpressing AREB1 or AREB1∆QT show improved drought tolerance. In our studies, soybean plants overexpressing AREB1∆QT were characterized molecularly, and the phenotype and drought response of three lines were accessed under greenhouse conditions. Under conditions of water deficit, the transformed plants presented a higher survival rate (100%) than those of their isoline, cultivar BR 16 (40%). Moreover, the transformed plants displayed better water use efficiency and had a higher number of leaves than their isoline. Because the transgenic plants had higher stomatal conductance than its isoline under well-watered conditions, it was suggested that the enhanced drought response of AREB1∆QT soybean plants might not be associated with altered transpiration rates mediated by ABA-dependent stomatal closure. However, it is possible that the smaller leaf area of the transgenic plants reduced their transpiration and water use, causing delayed stress onset. The difference in the degree of wilting and percentage of survival between the 35S-AREB1∆QT and wildtype plants may also be related to the regulation of genes that protect against dehydration because metabolic impairment of photosynthesis, deduced by an increasing internal CO 2 concentration, was not observed in the transgenic plants.