Functional Analysis Of The Arabidopsis WXR1,WXR3 Proteins During The Starch Metabolism

Starch is one of the most wide forms that plant store photosynthesis products, and plays very important roles in plant growth and development. Plants accumulate starch in chloroplasts via photosynthesis during the day, and degrade starch efficiently during the night to provide substance and energy for plant metabolism. In this dissertation, we studied the possible mechanism that WXRl and WXR3 (Weak Auxin Response) proteins are involved in starch metabolism from the perspective of genetics, cellular and molecular biology. Our data shows that the WXR1 and WXR3 protein possiblely regulate the starch metabolism by an unknown pathway:1) The treatment of different concentrations of glucose and different illumination time on the mutants showed that both mutations in WXR1 and WXR3 lead to restrained growth in normal light intensity and medium sugar concentration, suggesting that the normal energy supply produces inhibitory effect to the mutant; 2) Larger starch granules accumulate in the mutant chloroplasts were observed and almost couldn't be degraded during the night, indicating that WXR1 and WXR3 proteins may take part in starch degradation and utilization in plants; 3) The circadian rhythm expression of WXR1 and WXR3 showed the highest expression level at the end of day and the lowest expression at the end of night, while the expression level of SEX1 and SEX4 required in the starch degradation are significantly increased in the mutants. This result also suggests that both proteins may be associated with starch degradation activity; 4) The Q-PCR data of HXK1 and TOR suggested that the sugar signal was up-regulated in the mutants, indicating that the free sugar likely accumulates in the mutant plants; 5) The two-yeast hybrid experiments showed that there are indirect interactions among WXR1, WXR3 and K+ efflux protein KEAs mediated by RUS3 nad RUS5. As a consequence, we propose that WXR1 and WXR3 may promote starch degradation and utilization by regulating the K+ concentration and pH in chloroplasts, and play important roles in the regulation of plant growth and development.