Calmodulin-like (CML) proteins are important Ca2+ sensors, which play significant role in mediating plant stress tolerance. In the present study, cold responsive calmodulin-like (ShCML44) gene was isolated from cold tolerant wild tomato (Solanum habrochaites), and functionally characterized. The ShCML44 was differentially expressed in all plant tissues including root, stem, leaf, flower and fruit, and was strongly up-regulated under cold, drought and salinity stresses along with plant growth hormones. Under cold stress, progressive increase in the expression of ShCML44 was observed particularly in cold-tolerant S. habrochaites. The ShCML44-overexpressed plants showed greater tolerance to cold, drought, and salinity stresses, and recorded higher germination and better seedling growth. Transgenic tomato plants demonstrated higher antioxidant enzymes activity, gas exchange and water retention capacity with lower malondialdehyde accumulation and membrane damage under cold and drought stresses compared to wild-type. Moreover, transgenic plants exhibited reduced reactive oxygen species and higher relative water contents under cold and drought stress, respectively. Greater stress tolerance of transgenic plants was further reflected by the up-/down-regulation of stress-related genes including SOD, GST, CAT, POD, LOX, PR and ERD. In crux, these results strengthen the molecular understanding of ShCML44 gene to improve the abiotic stress tolerance in tomato.
RING finger proteins play an important role in plant adaptation to abiotic stresses. In the present study, a wild tomato (Solanum habrochaites) cold-induced RING-H2 finger gene, ShATL78L, was isolated, which has been identified as an abiotic stress responsive gene in tomato. The results showed that ShATL78L was constitutively expressed in various tissues such as root, leaf, petiole, stem, flower, and fruit. Cold stress up-regulated ShATL78L in the cold-tolerant S. habrochaites compared to the susceptible cultivated tomato (S. lycopersicum). Furthermore, ShATL78L expression was also regulated under different stresses such as drought, salt, heat, wound, osmotic stress, and exogenous hormones. Functional characterization showed that cultivated tomato overexpressing ShATL78L had improved tolerance to cold, drought and oxidative stresses compared to the wild-type and the knockdown lines. To understand the underlying molecular mechanism of ShATL78L regulating abiotic stress responses, we performed yeast one-hybrid and two-hybrid assays and found that RAV2 could bind to the promoter of ShATL78L and activates/alters its transcription, and CSN5B could interact with ShATL78L to regulate abiotic stress responses. Taken together, these results show that ShATL78L plays an important role in regulating plant adaptation to abiotic stresses through bound by RAV2 and interacting with CSN5B.Highlight: RAV2 binds to the promoter of ShATL78L to activates/alters its transcription to adapt the environmental conditions; furthermore, ShATL78L interacts with CSN5B to regulate the stress tolerance.
Seed germination determines when life starts in plants, plays an important role in the efficiency of agricultural production. Nonetheless, our knowledge of the mechanisms that regulate seed germination is limited. Here, we identified a novel gene that encodes mitogen-activated protein kinase 11 (MAPK11), which the expression level in seeds of tomatoes with low germination was significantly higher than that with high germination at room temperature. Overexpression of MAPK11 in TS-9—one accession with the optimum temperature for seed germination at 25 °C—led to a decrease in seed germination, and RNA interference of MAPK11 in TS-34—one accession with the optimum temperature for seed germination at 15 °C—induced increased seed germination at room temperature. Furthermore, we found that lines overexpressing MAPK11 exhibited hypersensitivity to ABA during seed germination. These observations are at least partially explained by our finding that MAPK11 upregulates both NCED1 expression and ABA biosynthesis and that MAPK11 affects ABA signaling and negatively regulates seed germination by influencing the phosphorylation of SnRK2.2 in vivo. In addition, we found that MAPK11 may possibly inhibit SnRK1 activation by binding and phosphorylating SnRK1 in vivo. SnRK1 interacts with ABI5 and suppresses the transcription of ABI5, which contributes to ABA signaling and regulates seed germination in tomato. Thus, our findings demonstrate that in tomato, a mechanism that depends on MAPK11 phosphorylating SnRKs affects ABA signaling and ultimately influences seed germination.
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