RESUMEN
Cyclic nucleotide-gated channels (CNGCs) have been implicated in diverse aspects of plant growth and development, including responses to biotic and abiotic stress, as well as pollen tube growth and fertility. Here, genetic evidence identifies CNGC16 in Arabidopsis (Arabidopsis thaliana) as critical for pollen fertility under conditions of heat stress and drought. Two independent transfer DNA disruptions of cngc16 resulted in a greater than 10-fold stress-dependent reduction in pollen fitness and seed set. This phenotype was fully rescued through pollen expression of a CNGC16 transgene, indicating that cngc16-1 and 16-2 were both loss-of-function null alleles. The most stress-sensitive period for cngc16 pollen was during germination and the initiation of pollen tube tip growth. Pollen viability assays indicate that mutant pollen are also hypersensitive to external calcium chloride, a phenomenon analogous to calcium chloride hypersensitivities observed in other cngc mutants. A heat stress was found to increase concentrations of 3',5'-cyclic guanyl monophosphate in both pollen and leaves, as detected using an antibody-binding assay. A quantitative PCR analysis indicates that cngc16 mutant pollen have attenuated expression of several heat-stress response genes, including two heat shock transcription factor genes, HsfA2 and HsfB1. Together, these results provide evidence for a heat stress response pathway in pollen that connects a cyclic nucleotide signal, a Ca(2+)-permeable ion channel, and a signaling network that activates a downstream transcriptional heat shock response.
Asunto(s)
Adaptación Fisiológica/genética , Proteínas de Arabidopsis/genética , Canales Catiónicos Regulados por Nucleótidos Cíclicos/genética , Tubo Polínico/genética , Polen/genética , Adaptación Fisiológica/efectos de los fármacos , Proteínas de Arabidopsis/metabolismo , Secuencia de Bases , Cloruro de Calcio/farmacología , GMP Cíclico/metabolismo , Canales Catiónicos Regulados por Nucleótidos Cíclicos/metabolismo , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Sequías , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Factores de Transcripción del Choque Térmico , Proteínas de Choque Térmico/genética , Proteínas de Choque Térmico/metabolismo , Calor , Datos de Secuencia Molecular , Mutación , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas Modificadas Genéticamente , Polen/crecimiento & desarrollo , Polen/metabolismo , Tubo Polínico/crecimiento & desarrollo , Tubo Polínico/metabolismo , Reproducción/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Estrés Fisiológico , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Stomata of most plants close to preserve water when the demand for CO2 by photosynthesis is reduced. Stomatal responses are slow compared with photosynthesis, and this kinetic difference erodes assimilation and water-use efficiency under fluctuating light. Despite a deep knowledge of guard cells that regulate the stoma, efforts to enhance stomatal kinetics are limited by our understanding of its control by foliar CO2. Guided by mechanistic modelling that incorporates foliar CO2 diffusion and mesophyll photosynthesis, here we uncover a central role for endomembrane Ca2+ stores in guard cell responsiveness to fluctuating light and CO2. Modelling predicted and experiments demonstrated a delay in Ca2+ cycling that was enhanced by endomembrane Ca2+-ATPase mutants, altering stomatal conductance and reducing assimilation and water-use efficiency. Our findings illustrate the power of modelling to bridge the gap from the guard cell to whole-plant photosynthesis, and they demonstrate an unforeseen latency, or 'carbon memory', of guard cells that affects stomatal dynamics, photosynthesis and water-use efficiency.