Differential regulation of jasmonate responses in multiple jaz mutants

Review: Losing JAZ4 for growth and defense

JAZ proteins are involved in the regulation of the jasmonate signaling pathway, which is responsible for various physiological processes, such as defense response, adaptation to abiotic stress, growth, and development in Arabidopsis. The conserved domains of JAZ proteins can serve as binding sites for a broad array of regulatory proteins and the diversity of these protein-protein pairings result in a variety of functional outcomes. Plant growth and defense are two physiological processes that can conflict with each other, resulting in undesirable plant trade-offs. Recent observations have revealed a distinguishing feature of JAZ4; it acts as negative regulator of both plant immunity and growth and development. We suggest that these complex biological processes can be decoupled at the JAZ4 regulatory node, due to prominent expression of JAZ4 in specific tissues and organs. This spatial separation of actions could explain the increased disease resistance and size of the plant root and shoot in the absence of JAZ4. At the tissue level, JAZ4 could play a role in crosstalk between hormones such as ethylene and auxin to control organ differentiation. Deciphering biding of JAZ4 to specific regulators in different tissues and the downstream responses is key to unraveling molecular mechanisms toward developing new crop improvement strategies.

A molecular framework for signaling crosstalk between jasmonate and ethylene in anthocyanin biosynthesis, trichome development, and defenses against insect herbivores in Arabidopsis

The phytohormones ethylene (ET) and jasmonate (JA) regulate plant development, growth, and defense responses; however, the molecular basis for their signaling crosstalk is unclear. Here, we show that JA-ZIM-domain (JAZ) proteins, which repress JA signaling, repress trichome initiation/branching and anthocyanin accumulation, and inhibit the transcriptional activity of the basic helix-loop-helix (bHLH)-MYB members (GLABRA3 (GL3)-GL1 and TRANSPARENT TESTA 8 (TT8)-MYB75) of WD-repeat/bHLH/MYB (WBM) complexes. The ET-stabilized transcription factors ETHYLENE-INSENSITIVE3 (EIN3) and EIN3-LIKE1 (EIL1) were found to bind to several members of WBM complexes, including GL3, ENHANCER OF GLABRA3 (EGL3), TT8, GL1, MYB75, and TRANSPARENT TESTA GLABRA1 (TTG1). This binding repressed the transcriptional activity of the bHLH-MYB proteins and inhibited anthocyanin accumulation, trichome formation, and defenses against insect herbivores while promoting root hair formation. Conversely, the JA-activated bHLH members GL3, EGL3, and TT8 of WBM complexes were able to interact with and attenuate the transcriptional activity of EIN3/EIL1 at the HOOKLESS1 promoter, and their overexpression inhibited apical hook formation. Thus, this study demonstrates a molecular framework for signaling crosstalk between JA and ET in plant development, secondary metabolism, and defense responses.

Comparative Transcriptome and Interaction Protein Analysis Reveals the Mechanism of IbMPK3-Overexpressing Transgenic Sweet Potato Response to Low-Temperature Stress

The sweet potato is very sensitive to low temperature. Our previous study revealed that IbMPK3-overexpressing transgenic sweet potato (M3) plants showed stronger low-temperature stress tolerance than wild-type plants (WT). However, the mechanism of M3 plants in response to low-temperature stress is unclear. To further analyze how IbMPK3 mediates low-temperature stress in sweet potato, WT and M3 plants were exposed to low-temperature stress for 2 h and 12 h for RNA-seq analysis, whereas normal conditions were used as a control (CK). In total, 3436 and 8718 differentially expressed genes (DEGs) were identified in WT at 2 h (vs. CK) and 12 h (vs. CK) under low-temperature stress, respectively, whereas 1450 and 9291 DEGs were detected in M3 plants, respectively. Many common and unique DEGs were analyzed in WT and M3 plants. DEGs related to low temperature were involved in Ca²⁺ signaling, MAPK cascades, the reactive oxygen species (ROS) signaling pathway, hormone transduction pathway, encoding transcription factor families (bHLH, NAC, and WRKY), and downstream stress-related genes. Additionally, more upregulated genes were associated with the MAPK pathway in M3 plants during short-term low-temperature stress (CK vs. 2 h), and more upregulated genes were involved in secondary metabolic synthesis in M3 plants than in the WT during the long-time low-temperature stress treatment (CK vs. 12 h), such as fatty acid biosynthesis and elongation, glutathione metabolism, flavonoid biosynthesis, carotenoid biosynthesis, and zeatin biosynthesis. Moreover, the interaction proteins of IbMPK3 related to photosynthesis, or encoding CaM, NAC, and ribosomal proteins, were identified using yeast two-hybrid (Y2H). This study may provide a valuable resource for elucidating the sweet potato low-temperature stress resistance mechanism, as well as data to support molecular-assisted breeding with the IbMPK3 gene.