Overexpression and interactions of Arabidopsis thaliana RAV1 (Related to Abscisic Acid Insensitive 3/ Viviparous 1), RAV2, RAV2-Like and ABI5 in transgenic cotton (Gossypium hirsutum): Effects on drought avoidance and fiber quality
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Plants have evolved complex overlapping response pathways for stresses such as drought, salt, cold, as well as hormonal cues such as abscisic acid (ABA). In this study, reverse genetics (knockout mutants) and overexpression of RAV (B3 domain) transcription factors suggested they could function as positive effectors of ABA response in seeds, roots, and leaves and delay flowering time. RAVs are highly induced at the transcript level by drought treatment, and AtRAV overexpression studies in cotton resulted in drought resistance due to biomass accumulation in lateral roots, more leaf area, delayed flowering, and higher water use efficiency under deficit irrigation in the field. Transgenic cotton plants had longer internodes and more stem weight. Unexpectedly, overexpression of RAVs leads to significant increases in fiber length. Repression of Gh Flowering Locus T by RAVs resulted in node positions 10-12 contributing to greater mass of cotton fibers than in wild type Coker 312 plants. Longer, more mature and finer fiber of RAVs transgenics resulted in better yarn production that has more tensile strength and has significantly fewer imperfections per unit length. ABI5 a basic leucine zipper TF (bZIP) functions in seeds and seedlings as a core component of ABA signaling. ABI5 transgenic cotton had more lateral root biomass that improved the water uptake and in conjunction with decreased stomatal conductance resulted in improved water use efficiency. ABI5 overexpression lines had significantly higher gin turn out in two independent lines under deficit and well-watered conditions on all the node positions studied. Stacking the B3 RAV and bZIP ABI5 TFS by crossing single transgenic lines of RAV1 or RAV2 plus ABI5 had additive or synergistic effects on late flowering, longer internode length, more fruit weight, and more root biomass. I interpret these results in the context of a “less stressed phenotype”. To test this hypothesis at the molecular level, I assayed drought- and reactive oxygen species (ROS)-inducible marker gene expression which provided evidence in support of the less stressed phenotypes.