Tomato phytochrome B1 modulates N, P, and K deficiency response by root-to-shoot communication

Phytochromes are involved in the expression of nutrient transporter genes and participate in signaling responses in plants under nutritional deficiency. This study investigated the reciprocal interaction between phytochrome B1 (phyB1) and N, P, and K deficiency responses, specifically focusing on shoot-root communication. For this purpose, we used grafting combinations of the control genotype (WT) with the tomato phyB1-deficient mutant ( phyB1 ) under nutritional sufficiency and individual deficiencies of N, P, and K. In nutrient-sufficient conditions, shoot phyB1 stimulates the uptake of N and P in the roots in addition to increase stomatal conductance, transpiration, and dry weight production, whereas root phyB1 regulated the production of chlorophyll in the shoot. With N deficiency, grafted plants with loss of shoot phyB1 function showed increased transpiration and less efficient water use. However, the WT/ phyB1 combination attenuated the damage caused by N deficiency by increasing the dry weight of the entire plant. Under P deficiency, the absence of root phyB1 decreased N uptake and increased malondialdehyde (MDA) production. However, the deficiency of phyB1 impaired the water-use efficiency of P-deficient plants. In K-deficient tomato, N and K uptake was under the control of both shoot and root phytochromes and shoot phyB1 regulated MDA production and increased photosynthesis. We conclude that phyB1 is involved in shoot-root communication for the control of nutritional, physiological, and growth responses in tomato, raising new roles of this photoreceptor and perspectives on the plant nutrition studies.