Mendel University in Brno 

Carbon control of shade avoidance responses in Arabidopsis

Archna Tiwari [a], Muhammed Jamsheer K. [a], Mohan Sharma [a], Harshita B. Saksena [a], Ashverya Laxmi [a]

[a] National Institute of Plant Genome Research, New Delhi, India-110067

Light is a crucial factor for plant growth and development. The reduction in photosynthetically active radiation leads to adaptive phenotypic responses such as hypocotyl and petiole elongation which ultimately help the plants to harness maximum light during competition. These responses are collectively known as Shade Avoidance Responses (SARs). Although, how light quality and quantity regulate SARs is highly explored, how the cellular sugar level, which is the ultimate product of light perception and photosynthesis, regulates this response is completely unknown. The SARs is highly costly in terms of plant fitness and seed production, therefore, an optimal response depending on the sugar level would ensure that plants do not commit their entire energy for SARs. We found that lower concentrations of glucose promote while higher concentration inhibited shade induced hypocotyl elongation. The lower concentration of glucose promoted auxin response which resulted in promotion of hypocotyl elongation. Higher concentration of glucose inhibited auxin response and promoted cytokinin signaling which is a potent negative regulator of cell elongation. Phytochromes, the red and far-red perceiving photoreceptors localize in discrete nuclear bodies (NBs) upon light illumination. The size of NBs is directly proportional to the activity of PHYB. In our study, we observed that low glucose leads to the accumulation of smaller while high glucose leads to larger PHYB NBs accumulation under normal as well as shade conditions. IAA and BAP work in an antagonistic manner, IAA inhibits while BAP promotes accumulation of PHYB NBs. Thus, our study highlights an important connection between cellular sugar status and hormonal signaling to fine-tune shade responses in plants.