Regulation of Arabidopsis photoreceptor CRY2 by two distinct E3 ubiquitin ligases

Abstract

Cryptochromes (CRYs) are photoreceptors or components of the molecular clock in various evolutionary lineages, and they are commonly regulated by polyubiquitination and proteolysis. Multiple E3 ubiquitin ligases regulate CRYs in animal models, and previous genetics study also suggest existence of multiple E3 ubiquitin ligases for plant CRYs. However, only one E3 ligase, Cul4COP1-SPAs, has been reported for plant CRYs so far. Here we show that Cul3LRBs is the second E3 ligase of CRY2 in Arabidopsis. We demonstrated the blue light-specific and CRY-dependent activity of LRBs (Light-Response Bric-a-Brack/Tramtrack/Broad 1, 2 & 3) in blue-light regulation of hypocotyl elongation. LRBs physically interact with photoexcited and phosphorylated CRY2 to facilitate polyubiquitination and degradation of CRY2 in response to blue light. We propose that Cul4COP1-SPAs and Cul3LRBs E3 ligases interact with CRY2 via different structure elements to regulate the abundance of CRY2 photoreceptor under different light conditions, facilitating optimal photoresponses of plants grown in nature.

UBP12 and UBP13 deubiquitinases destabilize the CRY2 blue-light receptor to regulate growth

“…We reasoned that one such candidate is the COP1 E3 ubiquitin ligase which is part of the CRL4 COP1-SPA complex. Previous studies have shown that COP1 is partially required for the turnover of CRY2 (Figure S5B) (Wang et al 2001;Lau et al 2019;Ponnu et al 2019;Weidler et al 2012;Wang et al 2015;Chen et al 2021).…”

“…During seedling emergence from the soil, in a developmental process called photomorphogenesis, CRYs control seedling stem growth relative to the amount of blue light perceived by them. This control of hypocotyl growth depends on the amount of blue light; a higher amount of light results in degradation of CRY2, leading to attenuation of its signaling, and a lower light amount results in accumulation of CRY2 (Pedmale et al 2016;Yu et al 2007;Chen et al 2021). CRY2 levels thus finetune growth in response to light levels; and so, it is essential to understand mechanisms that control CRY2 turnover.…”

“…In animals, F-box protein FBXL3 (F-box/LRR-repeat protein 3) functions as an E3 ubiquitin ligase to facilitate ubiquitination and degradation of mammalian CRY1 and CRY2 (Siepka et al 2007;Busino et al 2007;Godinho et al 2007). Recently, it was shown CRL4 COP1-SPA and CRL3 LRBs are required for the degradation of CRY2 in Arabidopsis (Weidler et al 2012;Liu et al 2016;Lau et al 2019;Ponnu et al 2019;Chen et al 2021). But the mechanism of action on how photoactive CRY2 is ubiquitinated by COP1 in light remains poorly understood, as they interact both in the dark and light and irrespective of CRY2's phosphorylation status (Wang et al 2001;Chen et al 2021).…”