Large-scale Proteomics Combined with Transgenic Experiments Demonstrates An Important Role of Jasmonic Acid in Potassium Deficiency Response in Wheat and Rice

Potassium (K(+)) is the most abundant inorganic cation in plants, and molecular dissection of K(+) deficiency has received considerable interest in order to minimize K(+) fertilizer input and develop high quality K(+)-efficient crops. However, the molecular mechanism of plant responses to K(+) deficiency is still poorly understood. In this study, 2-week-old bread wheat seedlings grown hydroponically in Hoagland solution were transferred to K(+)-free conditions for 8 d, and their root and leaf proteome profiles were assessed using the iTRAQ proteome method. Over 4000 unique proteins were identified, and 818 K(+)-responsive protein species showed significant differences in abundance. The differentially expressed protein species were associated with diverse functions and exhibited organ-specific differences. Most of the differentially expressed protein species related to hormone synthesis were involved in jasmonic acid (JA) synthesis and the upregulated abundance of JA synthesis-related enzymes could result in the increased JA concentrations. Abundance of allene oxide synthase (AOS), one key JA synthesis-related enzyme, was significantly increased in K(+)-deficient wheat seedlings, and its overexpression markedly increased concentrations of K(+) and JA, altered the transcription levels of some genes encoding K(+)-responsive protein species, as well as enhanced the tolerance of rice plants to low K(+) or K(+) deficiency. Moreover, rice AOS mutant (osaos) exhibited more sensitivity to low K(+) or K(+) deficiency. Our findings could highlight the importance of JA in K(+) deficiency, and imply a network of molecular processes underlying plant responses to K(+) deficiency.