|Wang, Xuewen -|
|Roig-Villanova, Irma -|
|Khan, Safina -|
|Quail, Peter -|
|Martinez-Garcia, Jaime -|
|Devlin, Paul -|
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 14, 2011
Publication Date: May 1, 2011
Citation: Wang, X., Roig-Villanova, I., Khan, S., Quail, P.H., Martinez-Garcia, J.F., Devlin, P.F. 2011. A novel high-throughput in vivo molecular screen for shade. Journal of Experimental Botany. 62:2973-2987. Interpretive Summary: Plants anticipate and avoid being shaded by other plants by starting a shade avoidance syndrome that involves growth elongation. In this work a screen was performed to identify plants that show no shade avoidance, and a new genetic alteration was found in the phyA gene that controls light responses. The phyA alteration also interfered with signaling through the related phyB pathway, leading to the hypothesis that the altered residue represents a key difference between the phyA and phyB protein forms.
Technical Abstract: The shade avoidance syndrome (SAS) allows plants to anticipate and avoid shading by neighbouring plants by initiating an elongation growth response. The phytochrome photoreceptors are able to detect a reduction in the red:far red ratio in incident light, the result of selective absorption of red and blue wavelengths by proximal vegetation. A shade-responsive luciferase reporter line (PHYB::LUC) was used to carry out a high-throughput screen to identify novel SAS mutants. The dracula 1 (dra1) mutant, that showed no avoidance of shade for the PHYB::LUC response, was the result of a mutation in the PHYA gene. Like previously characterized phyA mutants, dra1 showed a long hypocotyl in far red light and an enhanced hypocotyl elongation response to shade. However, dra1 additionally showed a long hypocotyl in red light. Since phyB levels are relatively unaffected in dra1, this gain-of-function red light phenotype strongly suggests a disruption of phyB signalling. The dra1 mutation, G773E within the phyA PAS2 domain, occurs at a residue absolutely conserved among phyA sequences. The equivalent residue in phyB is absolutely conserved as a threonine. PAS domains are structurally conserved domains involved in molecular interaction. Structural modelling of the dra1 mutation within the phyA PAS2 domain shows some similarity with the structure of the phyB PAS2 domain, suggesting that the interference with phyB signalling may be the result of non-functional mimicry. Hence, it was hypothesized that this PAS2 residue forms a key distinction between the phyA and phyB phytochrome species.