High-temperature (HT) stress is a major environmental stress that limits plant growth and development. MAPK cascades play key roles in plant growth and stress signaling, but their involvement in the HT stress response is poorly understood. Here, we describe a 47-kD MBP-phosphorylated protein (p47-MBPK) activated in tomato () leaves under HT and identify it as SlMPK1 by tandem mass spectrometry analysis. Silencing of in transgenic tomato plants resulted in enhanced tolerance to HT, while overexpression resulted in reduced tolerance. Proteomic analysis identified a set of proteins involved in antioxidant defense that are significantly more abundant in RNA interference- plants than nontransgenic plants under HT stress. RNA interference- plants also showed changes in membrane lipid peroxidation and antioxidant enzyme activities. Furthermore, using yeast two-hybrid screening, we identified a serine-proline-rich protein homolog, SlSPRH1, which interacts with SlMPK1 in yeast, in plant cells, and in vitro. We demonstrate that SlMPK1 can directly phosphorylate SlSPRH1. Furthermore, the serine residue serine-44 of SlSPRH1 is a crucial phosphorylation site in the SlMPK1-mediated antioxidant defense mechanism activated during HT stress. We also demonstrate that heterologous expression of in Arabidopsis () led to a decrease in thermotolerance and lower antioxidant capacity. Taken together, our results suggest that SlMPK1 is a negative regulator of thermotolerance in tomato plants. SlMPK1 acts by regulating antioxidant defense, and its substrate SlSPRH1 is involved in this pathway.
Phosphorus (P) is an essential plant nutrient, and deficiency of P is one of the most important factors restricting maize yield. Therefore, it is necessary to develop a more efficient program of P fertilization and breeding crop varieties with enhanced Pi uptake and use efficiency, which required understanding how plants respond to Pi starvation. To understand how maize plants adapt to P-deficiency stress, we screened 116 inbred lines in the field and identified two lines, DSY2 and DSY79 that were extreme low-P resistant and sensitive, respectively. We further conducted physiological, transcriptomic, and proteomic studies using the roots of DSY2 and DSY79 under normal or low-P conditions. The results showed that the low-P resistant line, DSY2 had larger root length, surface area and volume, higher root vitality, as well as acid phosphatase activity as compared with the low-P sensitive line, DSY79 under the low-P condition. The transcriptomic and proteomic results suggest that dramatic more genes were induced in DSY2, including the plant hormone signaling, acid phosphatase, and metabolite genes, as compared with DSY79 after being challenged by low-P stress. The new insights generated in this study will be useful toward the improvement of P-utilize efficiency in maize.
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