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Title: The shade avoidance syndrome in Aribdopsis: the antoagonistic role of phytochrome A and B differentiates vegetation

Author
item MARTINEZ-GARCIA, J - Centre For Research On Sustainable Agricultural Production Systems,cipav
item GALLEMI, M - Centre For Research On Sustainable Agricultural Production Systems,cipav
item MOLINA-CONTRERAS, M - Centre For Research On Sustainable Agricultural Production Systems,cipav
item LLORENTE, B - Centre For Research On Sustainable Agricultural Production Systems,cipav
item BEVILAQUA, M - Centre For Research On Sustainable Agricultural Production Systems,cipav
item QUAIL, P - University Of California

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2014
Publication Date: 10/21/2014
Citation: Martinez-Garcia, J., Gallemi, M., Molina-Contreras, M.J., Llorente, B., Bevilaqua, M.R., Quail, P.H. 2014. The shade avoidance syndrome in Aribdopsis: the antoagonistic role of phytochrome A and B differentiates vegetation. PLoS One. 9(10):e109275.

Interpretive Summary: The shade avoidance syndrome (SAS) refers to a set of plant responses aimed at adapting plant growth and development to high plant density environments, like those found in forests, prairies or crops. Two related but different situations can occur in these environments: neighboring plant proximity (without direct vegetative shading) and direct plant canopy shade from neighbors. Plants detect the presence of such neighbors, which will, or do already, compete for photosynthetically active sunlight, using the phytochrome (phy) photosensory receptor system. This paper shows that plants distinguish between the presence of proximal, but non-shading, neighbors, and direct foliar shade, using two different phy family members, phyA and phyB, which act antagonistically to control the growth response. This dual-track mechanism provides young seedlings with the capacity for both rapid elongation upon sensing of impending competition (the ‘‘neighbor-detection response mode’’), and attenuation of potentially deleterious excessive elongation upon direct interception of light by canopy shade (the ‘‘direct-shade response mode’’).

Technical Abstract: Light limitation caused by dense vegetation is one of the greatest threats to plant survival in natural environments. Plants detect such neighboring vegetation as a reduction in the red to far-red ratio (R:FR) of the incoming light. The low R:FR signal, perceived by phytochromes, initiates a set of responses collectively known as the shade avoidance syndrome, intended to reduce the degree of current or future shade from neighbors by overtopping such competitors or inducing flowering to ensure seed production. At the seedling stage these responses include increased hypocotyl elongation. We have systematically analyzed the Arabidopsis seedling response and the contribution of phyA and phyB to perception of decreased R:FR, at three different levels of photosynthetically active radiation. Our results show that the shade avoidance syndrome, induced by phyB deactivation, is gradually antagonized by phyA, operating through the so-called FR-High Irradiance Response, in response to high FR levels in a range that simulates plant canopy shade. The data indicate that the R:FR signal distinguishes between the presence of proximal, but non-shading, neighbors and direct foliar shade, via a intrafamily photosensory attenuation mechanism that acts to suppress excessive reversion toward skotomorphogenic development under prolonged direct vegetation shade.