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 (Solanum lycopersicum) leaves under HT and identify it as SlMPK1 by tandem mass spectrometry analysis. Silencing of SlMPK1 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-SlMPK1 plants than nontransgenic plants under HT stress. RNA interference-SlMPK1 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 SlSPRH1 in Arabidopsis (Arabidopsis thaliana) 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.

High temperature (HT) is an important environmental factor affecting crops growth, development, and yield. Transcriptome and proteome technologies developed in recent years can provide deeper and more reliable data to decipher the mechanisms of HT response. In the present study, the transcriptome analysis with RNA sequencing (RNA‐Seq) and integrative analysis on obtained proteomic data were performed in tomato (Solanum lycopersicum) leaves under HT stress (42°C for 4 hr). In total, 3,531 differentially expressed genes (DEGs) and 268 differentially expressed proteins (DEPs) were explored. The quantitative data were validated by qRT‐PCR and parallel reaction monitoring (PRM). Upon mapping of the DEGs/DEPs to the KEGG pathway database, “protein processing in the endoplasmic reticulum” was found to be the most significant enrichment pathway both at the transcriptional and protein levels, suggesting that endoplasmic reticulum stress may play a central role in HT tolerance. Furthermore, transcriptome‐proteome integrative analysis revealed 91 genes shared both in DEGs and DEPs, of which 79 correlations with the same changing trends were most associated with stress response and protein folding. Among these, a HT response gene designated SlBAG5 of unknown function received attention. The full‐length of SlBAG5 was cloned and ectopically overexpressed in Arabidopsis, which displayed thermosensitive phenotype. Taken together, this work provides deep insight into the molecular mechanisms of plant thermotolerance and also facilitates the identification of the key potential genes/proteins for HT response.

The Bemisia tabaci is a major leaf feeding insect pest to pepper (Capsicum annuum), causing serious damage to pepper growth and yield. It is particularly important to study the mechanism of pepper resistance to B. tabaci, and to breed and promote the varieties of pepper resistant to B. tabaci. However, very limited molecular mechanism is available about how plants perceive and defend themselves from the destructive pest. Proteome technologies have provided an idea method for studying plant physiological processes in response to B. tabaci. Here, a highly resistant genotype and a highly susceptible genotype were exposed to B. tabaci feeding for 48 h to explore the defense mechanisms of pepper resistance to B. tabaci. The proteomic differences between both genotypes were compared using isobaric tag for relative and absolute quantification (iTRAQ). The quantitative data were validated by parallel reaction monitoring (PRM). The results showed that 37 differential abundance proteins (DAPs) were identified in the RG (resistant genotype), while 17 DAPs were identified in the SG (susceptible genotype) at 48 h after B. tabaci feeding. 77 DAPs were identified when comparing RG with SG without feeding. The DAP functions were determined for the classification of the pathways, mainly involved in redox regulation, stress response, protein metabolism, lipid metabolism and carbon metabolism. Some candidate DAPs are closely related to B. tabaci resistance such as annexin D4-like (ANN4), calreticulin-3 (CRT3), heme-binding protein 2-like (HBP1), acidic endochitinase pcht28-like (PR3) and lipoxygenase 2 (LOX2). Taken together, this study indicates complex resistance-related events in B. tabaci interaction, provides novel insights into the molecular mechanism underlying the response of plant to B. tabaci, and identifies some candidate proteins against B. tabaci attack.