Abstract
Plants perceive red and far-red region of the light spectrum to regulate photomorphogenesis through a family of photoreceptors called phytochromes. Phytochromes transduce the light signals to trigger a cascade of downstream gene regulation in part via a subfamily of bHLH transcription factors called Phytochrome Interacting Factors (PIFs). As the repressors of light signaling pathways, most PIFs are phosphorylated and degraded through the ubiquitin/26S proteasome pathway in response to light. The mechanisms involved in the phosphorylation and degradation of PIFs have not been fully understood yet. Here we used an EMS mutagenesis and luminescent imaging system to identify mutants defective in the degradation of one of the PIFs, called PIF1. We identified five mutants named stable PIF (spf) that showed reduced degradation of PIF1 under light treatment in both luminescent imaging and immunoblot assays. The amounts of PIF1 in spf3, spf4, and spf5 were similar to a PIF1 missense mutant (PIF1–3M) that lacks interactions between PIF1 and phyA/phyB under light. The hypocotyl lengths of spf1 and spf2 were slightly longer under red light compared to the LUC-PIF1 control, while only spf1 displayed weak phenotype under far-red light conditions. Interestingly, the spf3, spf4, and spf5 displayed high abundance of PIF1, yet the hypocotyl lengths were similar to the wild type under these conditions. Cloning and characterization of these mutants will help identify key players in the light signaling pathways including, the light-regulated kinase(s) and the E3 ligase(s) necessary for the light-induced degradation of PIFs.
Highlights
Light is one of the most important factors for plant growth and development
Many studies have been conducted to understand phytochromes-Phytochrome Interacting Factors (PIFs) interaction and PIFs regulation on downstream target genes, but little is known about the factors necessary for the degradation of PIFs until recently, which is the key step in phytochrome-mediated light signaling pathway
Different phytochromes induce the degradation of PIFs with differential kinetics under red and/or far-red light conditions (Al-Sady et al, 2006; Shen et al, 2008)
Summary
Light is one of the most important factors for plant growth and development. As a sessile photosynthetic organism, plants are acutely sensitive to any environmental changes, such as light quality and quantity. When the young seedlings reach the surface of the soil, they are exposed to more light that changes the morphology of the seedlings with short hypocotyls, erected and expanded cotyledons, elongated roots and increased chlorophyll biosynthesis in a process called photomorphogenesis. The transition from skotomorphogenesis (etiolated seedling) to photomorphogenesis (de-etiolated seedling) under red/far-red light is spf Mutants in phy Signaling mainly mediated by a class of photoreceptor, called phytochrome (phy) (Rockwell et al, 2006; Bae and Choi, 2008; Wit et al, 2016). PhyA mutant is insensitive to far-red light for seedling de-etiolation, while phyB– phyE mainly functions under red light conditions (Franklin and Quail, 2010). Phytochromes form homo- and hetero-dimers among family members and regulate photomorphogenesis (Sharrock and Clack, 2004; Clack et al, 2009)
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