Analysis of Arabidopsis thaliana Red-Light Response Mutants Identified in a Genetic Enhancer Screen

Abstract

Plants require light for survival and have developed sophisticated pathways to respond and adapt to the light in their environment. Photoreceptors allow plants to sense specific wavelengths of light, one family being the red /far-red-absorbing phytochromes (phys). Phys have two conformations: inactive (Pr) and active (Pfr) forms. Absorption of red light promotes a shift to active Pfr, while far-red light absorption promotes assumption of inactive Pr 2. Pfr can also shift back to Pr independent of light (known as dark reversion). Upon activation by red light and transition to the Pfr form, the phytochromes are translocated into the nucleus from the cytosol to regulate gene expression. Work by our lab and others has shown two genes called Light-Response BTB 1 and 2 (LRB1 and LRB2) regulate the phy light-response pathway in the model plant Arabidopsis thaliana. LRB1 and LRB2 encode BTB (Bric-a-Brac, Tramtrack and Broad Complex) proteins that are target adaptors in E3 ubiquitin-ligase complexes that lead to the degradation of the phys through ubiquitylation under light treatment. Plants containing mutations within LRB genes (lrb1 lrb2 mutants) display hypersensitivity to red light due to elevated levels of the phys. To discover additional genes involved in light responses, previous members of the Gingerich lab conducted genetic enhancer screens utilizing the red light-hypersensitive lrb1 lrb2 mutants. They mutagenized lrb1 lrb2 seed with ethyl methanesulfonate (EMS) and identified individuals that exhibited further enhanced red light hypersensitivity. I have been working to map the mutations responsible for the highly increased red-light hypersensitivity in a subset of the lines. Our initial hope was that these mutations may occur in genes not previously known to be involved in light responses.