Abstract
Alterations in light quality significantly affect plant growth and development. In canopy shade, phytochrome photoreceptors perceive reduced ratios of red to far-red light (R:FR) and initiate stem elongation to enable plants to overtop competitors. This shade avoidance response is achieved via the stabilisation and activation of PHYTOCHROME INTERACTING FACTORs (PIFs) which elevate auxin biosynthesis. UV-B inhibits shade avoidance by reducing the abundance and activity of PIFs, yet the molecular mechanisms controlling PIF abundance in UV-B are unknown. Here we show that the UV-B photoreceptor UVR8 promotes rapid PIF5 degradation via the ubiquitin-proteasome system in a response requiring the N terminus of PIF5. In planta interactions between UVR8 and PIF5 are not observed. We further demonstrate that PIF5 interacts with the E3 ligase COP1, promoting PIF5 stabilisation in light-grown plants. Binding of UVR8 to COP1 in UV-B disrupts this stabilisation, providing a mechanism to rapidly lower PIF5 abundance in sunlight.
Highlights
Alterations in light quality significantly affect plant growth and development
UV-B can suppress residual shade avoidance responses in pif[4], pif[5] and pif[7] single and higher order mutants (Supplementary Fig. 1). These data suggest that the inhibition of shade avoidance by UV-B involves the suppression of PIF4, PIF5 and PIF7 activities
LerPIF5Ox 5-7, LerPIF5Ox 8–13 and uvr81PIF5ox 2-1 showed a long-hypocotyl when compared to Landsberg erecta (Ler) and uvr[] in continuous white light, whereas uvr8-1PIF5ox 1-3 resembled uvr[] controls (Supplementary Fig. 2a)
Summary
Phytochrome photoreceptors perceive reduced ratios of red to far-red light (R:FR) and initiate stem elongation to enable plants to overtop competitors. This shade avoidance response is achieved via the stabilisation and activation of PHYTOCHROME INTERACTING FACTORs (PIFs) which elevate auxin biosynthesis. 1234567890():,; In shade intolerant plants, the detection of neighbouring vegetation triggers a suite of developmental responses, termed shade avoidance These include the rapid elongation of stems to elevate leaves towards sunlight[1]. UV-B is perceived by dimers of the photoreceptor UV RESISTANCE LOCUS 8 (UVR8) These monomerise following UV-B absorption and interact with the CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1)/SUPPRESSOR OF PHYA-105 (SPA) complex, promoting the stabilisation and expression of ELONGATED HYPOCOTYL 5 (HY5) and HY5 HOMOLOG (HYH) which, in turn, drive UV-B-signalling[8]. PIF5 abundance is enhanced in uvr[8] mutants in UV-B and decreased in cop[1] mutants, suggesting that UVR8 binding to COP1 in UV-B acts to destabilise PIF5, rapidly inhibiting shade avoidance once sunlight has been reached
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