<i>AtDREB2A-CA</i> Influences Root Architecture and Increases Drought Tolerance in Transgenic Cotton

Abstract

Drought is a major environmental factor limiting cotton (Gossypium hirsutum L.) productivity worldwide and projected climate changes could increase their negative effects in the future. Thus, targeting the molecular mechanisms correlated with drought tolerance without reducing productivity is a challenge for plant breeding. In this way, we evaluated the effects of water deficit progress on AtDREB2A-CA transgenic cotton plant responses, driven by the stress-inducible rd29 promoter. Besides shoot and root morphometric traits, gas exchange and osmotic adjustment analyses were also included. Here, we present how altered root traits shown by transgenic plants impacted on physiological acclimation responses when submitted to severe water stress. The integration of AtDREB2A-CA into the cotton genome increased total root volume, surface area and total root length, without negatively affecting shoot morphometric growth parameters and nor phenotypic evaluated traits. Additionally, when compared to wild-type plants, transgenic plants (17-T 0 plants and its progeny) highlighted a gradual pattern of phenotypic plasticity to *These authors have contributed equally to this work. some photosynthetic parameters such as photosynthetic rate and stomatal conductance with water deficit progress. Transgene also promoted greater shoot development and root robustness (greater and deeper root mass) allowing roots to grow into deeper soil layers. The same morpho-physiological trend was observed in the subsequent generation (17.6-T 2 ). Our results suggest that the altered root traits shown by transgenic plants are the major contributors to higher tolerance response, allowing the AtDRE2A-CA-cotton plants to maintain elevated stomatal conductance and assimilate rates and, consequently, reducing their metabolic costs involved in the antioxidant responses activation. These results also suggest that these morpho-physiological changes increased the number of reproductive structures retained per plant (26% higher) when compared with its non-transgenic counterpart. This is the first report of cotton plants overexpressing the AtDRE2A-CA transcription factor, demonstrating a morpho-physiological and yield advantages under drought stress, without displaying any yield penalty under irrigated conditions. The mechanisms by which the root traits influenced the acclimation of the transgenic plants to severe water deficit conditions are also discussed. These data present an opportunity to use this strategy in cotton breeding programs in order to improve drought adaptation toward better rooting features.

AtDREB2A Gene Expression Under Control of the Inducible Promoter and Virus 5’-untranslated Regions Improves Tolerance to Salinity in Nicotiana Tabacum

“…In this work the effect of the constitutive 35S CaMV promoter and the inducible promoter of the rd29A gene, and four 5'-UTR (5'PVY, 5'ARC1, 5'AMV or 5'TMV) as the enhancers of various origins and mechanisms of action were investigated on the expression of two transgenes encoding a full-length transcription factor AtDREB2A FL and its constitutively active form AtDREB2A CA in model plant N. tabacum v. Samsun NN. Our results confirmed the fact shown earlier [20], [23], [25] that the constitutively active form AtDREB2A CA gene without the sequence coding the negative regulatory domain (NRD) under control of the inducible rd29A promoter was the most suitable transgene for creating plants resistant to abiotic stress. After the tobacco plant transformation 9 and 26 transgenic lines expressing the full-length DREB2A-FL and the constitutively active DREB2A-CA, respectively, were obtained.…”

“…Resistance of plants transformed by the same DREB2A-CA gene from Arabidopsis thaliana to one or another stress was associated with the choice of plants used for gene modification. For example, plant tolerance to drought increased after the integration of AtDREB2A-CA into Arabidopsis, soybean, sugarcane or cotton genomes [19], [20], [23], [26]. Rosa chinensis plants over expressing AtDREB2A-CA exhibited tolerance to 300 mM NaCl [25].…”

“…The enhancer effect of mentioned 5' and 3'-UTRs has been shown for genes using a wheat cell-free system or as a result of transient expression in protoplasts or leaf disk transformation. But only 5'TMV widely used for stable gene expression in transgenic plants, including genes of transcription factors of DREB (DEHYDRATION-RESPONSIVE ELEMENT BINDING) performing vital regulatory roles in abiotic stress response in plants [18], [19], [20]- [22]. The over-expression of gene coding the one of these factors, DREB2A, in Arabidopsis, Rosa chinensis and several other transgenic plants such as maize, soybean and peanut resulted in improved stress tolerance [23]- [27].…”

“…In comparison with the constitutive promoter, the use of the inducible promoter of the rd29A (rd, responsive to desiccation) gene for the expression of the AtDREB2A transgene, in most cases, does not affect the delay in plant growth and development [19], [23], [28]. After transformation by DREB2A CA under control rd29A promoter the transgenic cotton plants were obtained with significant increase in the number of reproductive organs and an improvement in the architecture of the root system in addition to an increase in plant tolerance to drought [20].…”

Plasticity in Root Length and Volume Through the Alternate Wetting and Drying Water Management in Rice

“…At same time, these two genotypes showed higher grain yield across set of evaluated genotypes. The root plasticity shown by these two genotypes allowed them to explore efficiently water and nutrients by its deepening in the soil profile (from zero to 20 cm depth, when a hardpan is found in our experimental station) whether compared to those without this plasticity capacity; which in turn, allowed them to maintain greater cell turgor and consequently, reduce its metabolic energetic costs involved in this pathways defense (e.g., osmotic adjustment and antioxidative mechanisms) (Lisei- de-Sá et al, 2017;Weber et al, 2014).…”