S-nitrosoglutathione Reductase-Mediated nitric oxide affects axillary buds outgrowth of solanum lycopersicum L. by regulating auxin and cytokinin signaling.

Auxin and cytokinin are two kinds of important phytohormones that mediate outgrowth of axillary buds in plants. How nitric oxide and its regulator of S-nitrosoglutathione reductase (GSNOR)taking part in auxin and cytokinin signaling for controlling axillary buds outgrowth remains elusive. We explained roles of GSNOR during tomato axillary buds outgrowth by physiological, biochemical and genetic approach. GSNOR negatively regulated NO homeostasis. Suppression of GSNOR promoted axillary buds outgrowth via inhibiting the expression of FZY in both apical and axillary buds. Meanwhile, AUX1 and PIN1 were down-regulated in apical buds but up-regulated in axillary buds in GSNOR-suppressed plants. Thus, reduced IAA accumulation was shown in both apical buds and axillary buds of GSNOR-suppressed plants. GSNOR-mediated changes of NO and auxin affected cytokinin biosynthesis, transport, and signaling. And a decreased ratio of auxin: cytokinin was shown in axillary buds of GSNOR-suppressed plants, leading to buds dormancy breaking. We also found that the original NO signaling was generated by nitrate reductase (NR)catalyzing nitrate as substrate. NR-mediated NO reduced the GSNOR activity through S-nitrosylation of Cys-10, then induced a further NO burst, which played the above roles to promote axillary buds outgrowth. Together, GSNOR-mediated NO played important roles in controlling axillary buds outgrowth via altering the homeostasis and signaling of auxin and cytokinin in tomato plants.