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-T0 plants and its progeny) highlighted a gradual pattern of phenotypic plasticity tosome 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-T2). 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.
Highlights
Drought is often the most yield-limiting factor for plants
We evaluated the effects of water deficit progress on AtDREB2A-CA transgenic cotton plant responses, driven by the stress-inducible rd29 promoter
Genomic DNA was extracted from leaves of the surviving transgenic plants and was used for PCR analysis to verify the presence of AtDREB2A-CA
Summary
Drought is often the most yield-limiting factor for plants. Water supplies will continue to decrease worldwide as the global population will increase from the current 7 billion to over 9 billion people in 2050 [1]. It is imperative to maximize food production vertically, e.g., to minimize the use of cropland and water use and develop higher-yielding varieties resistant to pests and diseases, as well as more tolerant to future climate scenarios [3] [4] Facing these global agricultural challenges, there is an urgent need to develop crops with delayed stress-onset to manage risk and increase yield and quality under both optimal and suboptimal conditions. Conventional breeding for water deficit tolerance has had and continues to have success, but it is labor-intensive and time-consuming These constraints primarily arise due to the complex identification of quantitative trait loci that controls yield, as well as the difficulty to control moisture levels in the field [7] [8] [9], which can lead to increase trial error, decreasing its precision and, making it difficult to quantify the treatment effects. Rapid progress in plant biotechnology has opened up new possibilities for creating drought tolerant crops by identifying key genes and introducing them through genetic engineering [10]
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