Genetic and Molecular Analysis of the Red-Light Response Pathway in Arabidopsis thaliana

Abstract

Plants 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-redabsorbing 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. 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, 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 (Figure 1)5,6. Plants containing mutations within LRB genes (lrb1-1 lrb2-1 mutants) display hypersensitivity to red light due to elevated levels of the phys. To discover additional genes involved in light responses, our lab conducted genetic enhancer screens utilizing the lrb1-1 lrb2-1 mutants, identifying individuals that exhibited further enhanced red light hypersensitivity. Here we detail our analysis of one of these enhancer lines, preliminarily called E2-1-2. In this line whole genome sequencing/mapping identified the putative enhancer mutation in the PHYB gene, which encodes the major phytochrome (phyB) involved in red light responses in Arabidopsis.