Study on mechanism of light and auxin mediated seedling growth and development in Arabidopsis thaliana

DoctorTwo main plant organ systems are the shoot and root system. Plant roots anchor the plant to the soil and absorb water and nutrients for growth. Shoot parts are mainly composed with leaf, flower, stem. Seedling stage is a good system to monitor responses of external and internal stimuli. We performed studies about shoot and root part growth and development of seedling by stimulus such as light and auxin related chemical. This thesis includes two main part of story. As a first part, root development was studied using chemical genetic approaches. Second, shoot parts (hypocotyls, leaf and petiole) were examined using reverse genetic approaches. Understanding the molecular mechanisms regulating root development is essential for improving plant survival and agricultural productivity. Extensive molecular genetic studies have provided important information on crucial components for the root development control over the last few decades. However, it is becoming difficult to identify new regulatory components in root development due to the functional redundancy and lethality of genes involved in root development. In this study, we performed a chemical genetic screen to identify novel synthetic compounds that regulate root development in Arabidopsis seedlings. The screen yielded a root growth inhibitor designated ‘rootin’, which inhibited Arabidopsis root development by modulating cell division and elongation, but did not significantly affect shoot development. Transcript analysis of phytohormone marker genes revealed that rootin preferentially altered the expression of auxin-regulated genes. Furthermore, rootin reduced the accumulation of PIN1, PIN3, and PIN7 proteins, and affected the auxin distribution in roots, which consequently may lead to the observed defects in root development. Our results suggest that rootin could be utilized to unravel the mechanisms underlying root development and to investigate dynamic changes in PIN-mediated auxin distribution. In plant life cycle, light is one of the most important factors. Light not only energy source for photosynthesis but also play pivotal roles as environment stimuli. Key players in light signal transduction include phytochromes, which act as photoreceptor. Here we used a one-step co-IP method to isolate the interactomes that form during different light conditions with the phytochromeB in a phyB-overexpressing transgenic Arabidopsis line. One of the interaction partners is nucleus-encoded chloroplast protein, ADG1. To reveal relationship between phyB and ADG1 protein, we observed location of ADG1 by GFP fusion. And the nucleus distribution of ADG1 also affected by phyB level and light quality. We also test photoresponses in loss-of function mutant. Fluence-rate response curves for inhibition of hypocotyls growth revealed that loss-of-function mutant were hyposensitive. Therefore, we suggest that chloroplast protein also have another function in nucleus. With the two stories, we conclude that light and auxin mediated seedling growth and development can be integrated with dynamic interaction with other signals in root and shoot parts. We further propose that how external and internal signals can be integrate into plant growth and development