Overexpression of AtNCED3 gene improved drought tolerance in soybean in greenhouse and field conditions

Water deficit is an important climatic problem that can impair agriculture yield and economy. Genetically modified soybean plants containing the AtNCED3 gene were obtained aiming drought-tolerance improvement. The NCED3 gene encodes a 9-cis-epoxycarotenoid dioxygenase (NCED, EC 1.13.11.51), an important enzyme in abscisic acid biosynthesis. ABA activates the expression of drought-responsive genes, in water-deficit conditions, targeting defense mechanisms and enabling plants to survive under low water availability. Results from greenhouse experiments showed that the transgene AtNCED3 and the endogenous genes GmAREB1, GmPP2C, GmSnRK2 and GmAAO3 presented higher expression under water deficit (WD) in the event 2Ha11 than in WT-plants. No significant correlation was observed between the plant materials and WD conditions for growth parameters; however, gas exchange measurements decreased in the GM event, which also showed 80% higher intrinsic water use when compared to WT plants. In crop season 2015/16, event 2Ha11 showed higher total number of pods, higher number of pods with seeds and yield than WT plants. ABA concentration was also higher in GM plants under WD. These results obtained in field screenings suggest that AtNCED3 soybean plants might outperform under drought, reducing economic and yield losses, thus being a good candidate line to be incorporated in the soybean-breeding program to develop drought-tolerant cultivars.

Phenotyping soybean plants transformed with rd29A:AtDREB1A for drought tolerance in the greenhouse and field

The development of drought tolerant plants is a high priority because the area suffering from drought is expected to increase in the future due to global warming. One strategy for the development of drought tolerance is to genetically engineer plants with transcription factors (TFs) that regulate the expression of several genes related to abiotic stress defense responses. This work assessed the performance of soybean plants overexpressing the TF DREB1A under drought conditions in the field and in the greenhouse. Drought was simulated in the greenhouse by progressively drying the soil of pot cultures of the P58 and P1142 lines. In the field, the performance of the P58 line and of 09D-0077, a cross between the cultivars BR16 and P58, was evaluated under four different water regimes: irrigation, natural drought (no irrigation) and water stress created using rain-out shelters in the vegetative or reproductive stages. Although the dehydration-responsive element-binding protein (DREB) plants did not outperform the cultivar BR16 in terms of yield, some yield components were increased when drought was introduced during the vegetative stage, such as the number of seeds, the number of pods with seeds and the total number of pods. The greenhouse data suggest that the higher survival rates of DREB plants are because of lower water use due to lower transpiration rates under well watered conditions. Further studies are needed to better characterize the soil and atmospheric conditions under which these plants may outperform the non-transformed parental plants.

Diurnal oscillations of soybean circadian clock and drought responsive genes

Rhythms produced by the endogenous circadian clock play a critical role in allowing plants to respond and adapt to the environment. While there is a well-established regulatory link between the circadian clock and responses to abiotic stress in model plants, little is known of the circadian system in crop species like soybean. This study examines how drought impacts diurnal oscillation of both drought responsive and circadian clock genes in soybean. Drought stress induced marked changes in gene expression of several circadian clock-like components, such as LCL1-, GmELF4- and PRR-like genes, which had reduced expression in stressed plants. The same conditions produced a phase advance of expression for the GmTOC1-like, GmLUX-like and GmPRR7-like genes. Similarly, the rhythmic expression pattern of the soybean drought-responsive genes DREB-, bZIP-, GOLS-, RAB18- and Remorin-like changed significantly after plant exposure to drought. In silico analysis of promoter regions of these genes revealed the presence of cis-elements associated both with stress and circadian clock regulation. Furthermore, some soybean genes with upstream ABRE elements were responsive to abscisic acid treatment. Our results indicate that some connection between the drought response and the circadian clock may exist in soybean since (i) drought stress affects gene expression of circadian clock components and (ii) several stress responsive genes display diurnal oscillation in soybeans.

Physiological parameters in sugarcane cultivars submitted to water deficit

To investigate the processes involved in the susceptibility of sugarcane plants to water deficit, several physiological parameters were evaluated in drought tolerant (SP83-2847 and CTC15) and sensitive (SP86-155) cultivars. The water deficit affected the photosynthetic apparatus of all the plants in different ways, within and among cultivars. The photosynthetic rate and stomatal conductance decreased significantly in all cultivars submitted to water deficit. In control plants of the tolerant cultivars (SP83-2847 and CTC15) the photosynthetic rate was higher than in the sensitive cultivar (SP86-155). Cultivar CTC15 showed the highest relative water content during the dry period. The quantum efficiency photosystem II of cultivar SP83-2847 was more stable in the last days of the experimental treatment, suggesting that the decline in relative water content stimulated an adjustment of photosynthetic capacity to tolerate the changes in water availability. As a whole, the tolerant SP83-2847 and CTC15 cultivars exhibited a better photosynthetic performance than the sensitive SP86-155 cultivar. The data suggest that these physiological parameters can be used in the evaluation and distinction of drought tolerant and sensitive sugarcane genotypes.

Are chemical compounds important for soybean resistance to Anticarsia gemmatalis?

The identification and quantification of flavonoids (rutin and genistin) present in extracts of soybean genotypes, and their effects on the biology and physiology of Anticarsia gemmatalis Hübner (Lep.: Noctuidae) were studied. Analysis of covariance and bicoordinate utilization plots were used to remove the effect of feeding time from pupal weight and consumption as well as to separate pre- and postingestive effects of treatment on A. gemmatalis growth. Genotypes PI 274454, PI 227687, and "IAC-100" extracts in general, caused higher mortality, negatively influenced initial larval and pupal weight, and elongated larval cycle. Larvae fed on the "IAC-100" extract diet ingested larger amounts of food per unit of time, but were less efficient in its conversion to biomass. Leaf extracts of PI 227687 had the largest concentration of rutin (quercitin 3-O-rhamnosylglucoside), followed by PI 274454, and "IAC-100"; PI 74454 also had the highest genistin (genistein 7-O-glucoside) content. The susceptible cultivar "BR-16" showed only a kaempferol-based flavonoid in its chemical profile, indicating that after successive crosses, secondary compounds responsible for plant defenses were eliminated. Genotypes PI 274454, PI 227687, and "IAC-100" showed accentuated resistance characteristics and were considered inadequate sources for the development of A. gemmatalis. Considering rutin and genistin concentration in these genotypes, it is suggested that flavonoids are important factors conferring resistance to A. gemmatalis.