Creation and Characterization of LRB (Light-Response BTB) / PIF (Phytochrome-Interacting Factor) Mutant Lines in Arabidopsis thaliana

Abstract

Light is vital to plant survival and thus plants have developed sophisticated pathways to respond properly to their light environments. Plants sense specific wavelengths of light via photoreceptors, one family of which are the red (R)/far-red (FR)-absorbing phytochromes (phys). Absorption of red light activates the phys, which causes their translocation from the cytosol to the nucleus where they modulate gene expression. They do so by regulating the activity and levels of a family of transcription factors called Phytochrome-Interacting Factors (PIFs). In response to red light, the active phys cause PIFs to be ubiquitylated and degraded, which activates expression of PIF-repressed genes. There is feedback regulation of this pathway as, in response to red light; the PIFs also induce ubiquitylation and degradation of the phys. Work by our lab and others has implicated two genes (called Light-Response BTB 1 and 2 [LRB1 and LRB2]) as critical regulators of the phy/PIF light-response pathway. LRB1 and LRB2 encode BTB (Bric-a-Brac, Tramtrack, Broad Complex) domain-containing proteins that act as target adapters in E3 ubiquitin-ligase complexes. Plants with disruptions of the LRB genes have reduced light-dependent degradation of phys and, like plants with disruptions of PIF genes, exhibit hypersensitivity to red light. The mechanism by which the LRBs modulate phy levels is not entirely clear, however a report published recently showed the LRBs can bind to a complex of a PIF protein (PIF3) and a phy (phyB), leading to ubiquitylation and degradation of both PIF3 and phyB. In order to better understand how the LRB and PIF genes interact we are taking a genetic approach, creating plants with disruptions of both LRB and PIF genes. Study of the phenotypes of these plants may shed light on how these two families of genes work together to regulate red light responses.