Shade Avoidance and the Regulation of Leaf Inclination in Rice

ABSTRACT: The shade avoidance syndrome is a morphologicaland physiological response when plants are exposed to shade. Recent work in Arabidopsis had begun to define the molecular components of the shade avoidance syndrome in dicotyledonous model plant. However, little is known about the shade avoidance response networks in agriculturally important monocotyledon crops such as rice. Here, we found that the degree of bending at the lamina joint is inversely proportional to the R:FR ratio. To elucidate which phytochrome is involved in this response, we did lamina joint inclination assay with the rice phytochrome-deficient mutants (osphyA, osphyB, and osphyC) and the wild type plants. Whereas the osphyA and osphyC knockout mutants bent at the lamina joint in the far-red rich condition as the wild type plants, the osphyB knockout mutants no longer bent at the lamina joint in the far-red rich condition. These results suggest that PHYB acts as a sole photoreceptor in the lamina joint inclination response in rice. Plant responses to shade (the reduced ratio of red light to far-red light) referred to as the shade avoidance syndrome (SAS). The phytochrome photoreceptors perceived R: FR ratio change, then control the adaptive responses such as stem elongation, leaf expansion, seed germination, leaf inclination, and flowering time