RESUMEN
Plants have evolved complex molecular, cellular and physiological mechanisms to respond to environmental stressors. Because of the inherent complexity of this response, genetic manipulation to substantially improve water deficit tolerance, particularly in agricultural crops, has been largely unsuccessful, as the improvements are frequently accompanied by slower growth and delayed reproduction. Here, we ectopically express two abiotic stress-responsive bZIP AREB/ABF transcription factor orthologs, Arabidopsis ABF3 and Gossypium hirsutum ABF2D, in G. hirsutum, to compare the effects of exogenous and endogenous AREB/ABF transgene overexpression on dehydration resilience. Our results show that ectopic expression of each of these orthologs increases dehydration resilience, although these increases are accompanied by slower growth. These phenotypic effects are proportional to the ectopic expression level in the GhABF2D transgenic plants, while the phenotypes of all of the AtABF3 transgenic plants are similar, largely independent of ectopic expression level, possibly indicating differential post-transcriptional regulation of these transgenes. Our results indicate that overexpression of exogenous and endogenous ABF homologs in G. hirsutum substantially increases drought resilience, primarily through stomatal regulation, negatively impacting transpiration and photosynthetic productivity.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/metabolismo , Gossypium/fisiología , Factores de Transcripción/metabolismo , Proteínas de Arabidopsis/genética , Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/genética , Productos Agrícolas , Sequías , Expresión Génica Ectópica , Gossypium/genética , Fenotipo , Fotosíntesis , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Estomas de Plantas/genética , Estomas de Plantas/fisiología , Transpiración de Plantas/fisiología , Plantas Modificadas Genéticamente , Estrés Fisiológico , Factores de Transcripción/genéticaRESUMEN
Gibberellic acid (GA) is both necessary and sufficient to promote fiber elongation in cultured fertilized ovules of the upland cotton variety Coker 312. This is likely due to the temporal and spatial regulation of GA biosynthesis, perception, and subsequent signal transduction that leads to alterations in gene expression and morphology. Our results indicate that the initiation of fiber elongation by the application of GA to cultured ovules corresponds with increased expression of genes that encode xyloglucan endotransglycosylase/hydrolase (XTH) and expansin (EXP) that are involved in promoting cell elongation. To gain a better understanding of the GA signaling components in cotton, that lead to such changes in gene expression, two GA receptor genes (GhGID1a and GhGID1b) and two DELLA protein genes (GhSLR1a and GhSLR1b) that are orthologous to the rice GA receptor (GID1) and the rice DELLA gene (SLR1), respectively, were characterized. Similar to the GA biosynthetic genes, expression of GhGID1a and GhGID1b is under the negative regulation by GA while GA positively regulates GhSLR1a. Recombinant GST-GhGID1s showed GA-binding activity in vitro that was augmented in the presence of GhSLR1a, GhSLR1b, or rice SLR1, indicating complex formation between the receptors and repressor proteins. This was further supported by the GA-dependent interaction of these proteins in yeast cells. Ectopic expression of the GhGID1a in the rice gid1-3 mutant plants rescued the GA-insensitive dwarf phenotype, which demonstrates that it is a functional GA receptor. Furthermore, ectopic expression of GhSLR1b in wild type Arabidopsis led to reduced growth and upregulated expression of DELLA-responsive genes.
Asunto(s)
Giberelinas/farmacología , Gossypium/metabolismo , Proteínas de Plantas/metabolismo , Transducción de Señal/efectos de los fármacos , Secuencia de Aminoácidos , Electroforesis en Gel de Poliacrilamida , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Gossypium/genética , Datos de Secuencia Molecular , Oryza/genética , Oryza/metabolismo , Reguladores del Crecimiento de las Plantas/farmacología , Proteínas de Plantas/genética , Proteínas de Plantas/fisiología , Unión Proteica , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de Aminoácido , Transducción de Señal/genética , Transducción de Señal/fisiología , Técnicas del Sistema de Dos HíbridosRESUMEN
Our current understanding of the role of phytohormones in the development of cotton fibers is derived largely from an amenable culture system in which cotton ovules, collected on the day of anthesis, are floated on liquid media. Under these conditions, supplemental auxin and gibberellin were found to promote fiber initiation and elongation. More recently, addition of low concentrations of the brassinosteroid brassinolide (BL) were also found to promote fiber elongation while a brassinosteroid biosynthesis inhibitor brassinazole2001 (Brz) inhibited fiber development. In order to elucidate the role of brassinosteroid in cotton fiber development further, we have performed a more detailed analysis of the effects of these chemicals on cultured cotton ovules. Our results confirm that exogenous BL promotes fiber elongation while treatment with Brz inhibits it. Furthermore, treatment of cotton floral buds with Brz results in the complete absence of fiber differentiation, indicating that BR is required for fiber initiation as well as elongation. Expression of fiber genes associated with cell elongation increased in ovules treated with BL and was suppressed by Brz treatment, establishing a correlation between brassinosteroid-regulated gene expression and fiber elongation. These results establish a clear connection between brassinosteroid and fiber development and open the door for genetic analysis of cotton development through direct modification of the brassinosteroid signal transduction pathway.