Plant drought tolerance is a complex trait that requires a global view to understand its underlying mechanism. The proteomic aspects of plant drought response have been extensively investigated in model plants, crops and wood plants. In this review, we summarize recent proteomic studies on drought response in leaves to reveal the common and specialized drought-responsive mechanisms in different plants. Although drought-responsive proteins exhibit various patterns depending on plant species, genotypes and stress intensity, proteomic analyses show that dominant changes occurred in sensing and signal transduction, reactive oxygen species scavenging, osmotic regulation, gene expression, protein synthesis/turnover, cell structure modulation, as well as carbohydrate and energy metabolism. In combination with physiological and molecular results, proteomic studies in leaves have helped to discover some potential proteins and/or metabolic pathways for drought tolerance. These findings provide new clues for understanding the molecular basis of plant drought tolerance.

The pathogen-responsive protein kinases CPK5/CPK6 and MPK3/MPK6 cooperatively regulate camalexin biosynthesis upon pathogen infection via differential phosphory

Camalexin, an indolic antimicrobial metabolite, is the major phytoalexin in Arabidopsis thaliana, and plays a crucial role in pathogen resistance. Our previous studies revealed that the Arabidopsis mitogen-activated protein kinases MPK3 and MPK6 positively regulate pathogen-induced camalexin biosynthesis via phosphoactivating the transcription factor WRKY33. Here, we report that the ethylene and jasmonate (JA) pathways act synergistically with the MPK3/MPK6–WRKY33 module at multiple levels to induce camalexin biosynthesis in Arabidopsis upon pathogen infection. The ETHYLENE RESPONSE FACTOR1 (ERF1) transcription factor integrates the ethylene and JA pathways to induce camalexin biosynthesis via directly upregulating camalexin biosynthetic genes. ERF1 also interacts with and depends on WRKY33 to upregulate camalexin biosynthetic genes, indicating that ERF1 and WRKY33 form transcriptional complexes to cooperatively activate camalexin biosynthetic genes, thereby mediating the synergy of ethylene/JA and MPK3/MPK6 signaling pathways to induce camalexin biosynthesis. Moreover, as an integrator of the ethylene and JA pathways, ERF1 also acts as a substrate of MPK3/MPK6, which phosphorylate ERF1 to increase its transactivation activity and therefore further cooperate with the ethylene/JA pathways to induce camalexin biosynthesis. Taken together, our data reveal the multilayered synergistic regulation of camalexin biosynthesis by ethylene, JA, and MPK3/MPK6 signaling pathways via ERF1 and WRKY33 transcription factors in Arabidopsis.