(The) role of REDUCED GRAVITROPIC 1 in regulating gravitropic responses in plants by forming starch granules

Abstract

In the dark, plants display hypocotyl negative gravitropism to reach the light. Plants red/far-red light receptor, phytochrome is known to regulate hypocotyl negative gravitropism. In light condition, activated phytochrome inhibits hypocotyl gravitropism by inhibiting starch-filled amyloplasts, which are important for gravity sensing in plants. In the dark, phytochrome is inactivated therefore, downstream transcription factor PIF1 maintains starchfilled amyloplasts and promotes hypocotyl gravitropism. To identify how PIF1 regulates amyloplast formation and hypocotyl gravitropism, we performed EMS mutagenesis, and isolated mutants which showed disrupted gravitropism. Among them, those that not only showed disrupted gravitropism but also had defect in amyloplast formation were named as rgv1. Through the whole-genome sequencing, RGV1 was allelic to previously reported ESV1 which is known to regulate starch accumulation at dawn. RGV1 exists in various starch-synthesizing organisms including rice, potato and even liverwort. We figured out these orthologs are functionally conserved. Also, in rice rgv1 mutant, starch accumulation in leaves, granule, and root was significantly decreased.