RESUMEN
Heterotrimeric GTP-binding proteins (G proteins) are a group of regulators essential for signal transmission into cells. Regulator of G protein signaling 1 (AtRGS1) possesses intrinsic GTPase-accelerating protein (GAP) activity and could suppress G protein and glucose signal transduction in Arabidopsis (Arabidopsis thaliana). However, how AtRGS1 activity is regulated is poorly understood. Here, we identified a knockout mutant of oxysterol binding protein-related protein 2A, orp2a-1, which exhibits similar phenotypes to the arabidopsis g-protein beta 1-2 (agb1-2) mutant. Transgenic lines overexpressing ORP2A displayed short hypocotyls, a hypersensitive response to sugar, and lower intracellular AtRGS1 levels than the control. Consistently, ORP2A interacted with AtRGS1 in vitro and in vivo. Tissue-specific expression of 2 ORP2A alternative splicing isoforms implied functions in controlling organ size and shape. Bioinformatic data and phenotypes of orp2a-1, agb1-2, and the orp2a-1 agb1-2 double mutant revealed the genetic interactions between ORP2A and Gß in the regulation of G protein signaling and sugar response. Both alternative protein isoforms of ORP2A localized in the endoplasmic reticulum (ER), plasma membrane (PM), and ER-PM contact sites and interacted with vesicle-associated membrane protein-associated protein 27-1 (VAP27-1) in vivo and in vitro through their two phenylalanines in an acidic track-like motif. ORP2A also displayed differential phosphatidyl phosphoinositide binding activity mediated by the pleckstrin homology domain in vitro. Taken together, the Arabidopsis membrane protein ORP2A interacts with AtRGS1 and VAP27-1 to positively regulate G protein and sugar signaling by facilitating AtRGS1 degradation.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Subunidades beta de la Proteína de Unión al GTP , Proteínas de Unión al GTP Heterotriméricas , Proteínas RGS , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Proteínas RGS/genética , Proteínas RGS/química , Proteínas RGS/metabolismo , Glucosa/metabolismo , Proteínas Portadoras/metabolismo , Transducción de Señal , Proteínas de Unión al GTP Heterotriméricas/metabolismo , Lípidos , Subunidades beta de la Proteína de Unión al GTP/genética , Subunidades beta de la Proteína de Unión al GTP/metabolismoRESUMEN
Transitory starch is the portion of starch that is synthesized during the day in the chloroplast and usually used for plant growth overnight. Here, we report altered metabolism of transitory starch in the wxr1/wxr3 (weak auxin response 1/3) mutants of Arabidopsis. WXR1/WXR3 were previously reported to regulate root growth of young seedlings and affect the auxin response mediated by auxin polar transport in Arabidopsis. In this study the wxr1/wxr3 mutants accumulated transitory starch in cotyledon, young leaf, and hypocotyl at the end of night. WXR1/WXR3 expression showed diurnal variation. Grafting experiments indicated that the WXRs in root were necessary for proper starch metabolism and plant growth. We also found that photosynthesis was inhibited and the transcription level of DIN1/DIN6 (Dark-Inducible 1/6) was reduced in wxr1/wxr3. The mutants also showed a defect in the ionic equilibrium of Na+ and K+, consistent with our bioinformatics data that genes related to ionic equilibrium were misregulated in wxr1. Loss of function of WXR1 also resulted in abnormal trafficking of membrane lipids and proteins. This study reveals that the plastid proteins WXR1/WXR3 play important roles in promoting transitory starch degradation for plant growth over night, possibly through regulating ionic equilibrium in the root.