Temperature modulation of CAMTA3 gene induction activity is mediated through the DNA binding domain

Molecular Mechanisms Underlying Freezing Tolerance in Plants: Implications for Cryopreservation

Cryopreservation is a crucial technique for the long-term ex situ conservation of plant genetic resources, particularly in the context of global biodiversity decline. This process entails freezing biological material at ultra-low temperatures using liquid nitrogen, which effectively halts metabolic activities and preserves plant tissues over extended periods. Over the past seven decades, a plethora of techniques for cryopreserving plant materials have been developed. These include slow freezing, vitrification, encapsulation dehydration, encapsulation-vitrification, droplet vitrification, cryo-plates, and cryo-mesh techniques. A key challenge in the advancement of cryopreservation lies in our ability to understand the molecular processes underlying plant freezing tolerance. These mechanisms include cold acclimatization, the activation of cold-responsive genes through pathways such as the ICE-CBF-COR cascade, and the protective roles of transcription factors, non-coding RNAs, and epigenetic modifications. Furthermore, specialized proteins, such as antifreeze proteins (AFPs) and late embryogenesis abundant (LEA) proteins, play crucial roles in protecting plant cells during freezing and thawing. Despite its potential, cryopreservation faces significant challenges, particularly in standardizing protocols for a wide range of plant species, especially those from tropical and subtropical regions. This review highlights the importance of ongoing research and the integration of omics technologies to improve cryopreservation techniques, ensuring their effectiveness across diverse plant species and contributing to global efforts regarding biodiversity conservation.

OsCAMTA3 Negatively Regulates Disease Resistance to Magnaporthe oryzae by Associating with OsCAMTAPL in Rice

Rice (Oryza sativa) is one of the most important staple foods worldwide. However, rice blast disease, caused by the ascomycete fungus Magnaporthe oryzae, seriously affects the yield and quality of rice. Calmodulin-binding transcriptional activators (CAMTAs) play vital roles in the response to biotic stresses. In this study, we showed that OsCAMTA3 and CAMTA PROTEIN LIKE (OsCAMTAPL), an OsCAMTA3 homolog that lacks the DNA-binding domain, functioned together in negatively regulating disease resistance in rice. OsCAMTA3 associated with OsCAMTAPL. The oscamta3 and oscamtapl mutants showed enhanced resistance compared to wild-type plants, and oscamta3/pl double mutants showed more robust resistance to M. oryzae than oscamta3 or oscamtapl. An RNA-Seq analysis revealed that 59 and 73 genes, respectively, were differentially expressed in wild-type plants and oscamta3 before and after inoculation with M. oryzae, including OsALDH2B1, an acetaldehyde dehydrogenase that negatively regulates plant immunity. OsCAMTA3 could directly bind to the promoter of OsALDH2B1, and OsALDH2B1 expression was decreased in oscamta3, oscamtapl, and oscamta3/pl mutants. In conclusion, OsCAMTA3 associates with OsCAMTAPL to regulate disease resistance by binding and activating the expression of OsALDH2B1 in rice, which reveals a strategy by which rice controls rice blast disease and provides important genes for resistance breeding holding a certain positive impact on ensuring food security.

Regulatory networks in plant responses to drought and cold stress

Drought and cold represent distinct types of abiotic stress, each initiating unique primary signaling pathways in response to dehydration and temperature changes, respectively. However, a convergence at the gene regulatory level is observed where a common set of stress-responsive genes is activated to mitigate the impacts of both stresses. In this review, we explore these intricate regulatory networks, illustrating how plants coordinate distinct stress signals into a collective transcriptional strategy. We delve into the molecular mechanisms of stress perception, stress signaling, and the activation of gene regulatory pathways, with a focus on insights gained from model species. By elucidating both the shared and distinct aspects of plant responses to drought and cold, we provide insight into the adaptive strategies of plants, paving the way for the engineering of stress-resilient crop varieties that can withstand a changing climate.

Arabidopsis Calmodulin-like Proteins CML13 and CML14 Interact with Calmodulin-Binding Transcriptional Activators and Function in Salinity Stress Response

Eukaryotic cells use calcium ions (Ca2+) as second messengers, particularly in response to abiotic and biotic stresses. These signals are detected by Ca2+ sensor proteins, such as calmodulin (CaM), which regulate the downstream target proteins. Plants also possess many CaM-like proteins (CMLs), most of which remain unstudied. We recently demonstrated that Arabidopsis CML13 and CML14 interact with proteins containing isoleucine/glutamine (IQ) domains, including CaM-binding transcriptional activators (CAMTAs). Here, we show that CaM, CML13 and CML14 bind all six members of the Arabidopsis CAMTA family. Using a combination of in planta and in vitro protein-interaction assays, we tested 11 members of the CaM/CML family and demonstrated that only CaM, CML13 and CML14 bind to CAMTA IQ domains. CaM, CML13 and CML14 showed Ca2+-independent binding to the IQ region of CAMTA6 and CAMTA3, and CAMTA6 in vitro exhibited some specificity toward individual IQ domains within CAMTA6 in split-luciferase in planta assays. We show that cml13 mutants exhibited enhanced salinity tolerance during germination compared to wild-type plants, a phenotype similar to camta6 mutants. In contrast, plants overexpressing CML13-GFP or CML14-GFP in the wild-type background showed increased NaCl sensitivity. Under mannitol stress, cml13 mutants were more susceptible than camta6 mutants or wild-type plants. The phenotype of cml13 mutants could be rescued with the wild-type CML13 gene. Several salinity-marker genes under CAMTA6 control were similarly misregulated in both camta6 and cml13 mutants, further supporting a role for CML13 in CAMTA6 function. Collectively, our data suggest that CML13 and CML14 participate in abiotic stress signaling as CAMTA effectors.

Identification and Molecular Characterization of the CAMTA Gene Family in Solanaceae with a Focus on the Expression Analysis of Eggplant Genes under Cold Stress

Calmodulin-binding transcription activator (CAMTA) is an important calmodulin-binding protein with a conserved structure in eukaryotes which is widely involved in plant stress response, growth and development, hormone signal transduction, and other biological processes. Although CAMTA genes have been identified and characterized in many plant species, a systematic and comprehensive analysis of CAMTA genes in the Solanaceae genome is performed for the first time in this study. A total of 28 CAMTA genes were identified using bioinformatics tools, and the biochemical/physicochemical properties of these proteins were investigated. CAMTA genes were categorized into three major groups according to phylogenetic analysis. Tissue-expression profiles indicated divergent spatiotemporal expression patterns of SmCAMTAs. Furthermore, transcriptome analysis of SmCAMTA genes showed that exposure to cold induced differential expression of many eggplant CAMTA genes. Yeast two-hybrid and bimolecular fluorescent complementary assays suggested an interaction between SmCAMTA2 and SmERF1, promoting the transcription of the cold key factor SmCBF2, which may be an important mechanism for plant cold resistance. In summary, our results provide essential information for further functional research on Solanaceae family genes, and possibly other plant families, in the determination of the development of plants.

The amino acid region from 448-517 of CAMTA3 transcription factor containing a part of the TIG domain represses the N-terminal repression module function

CAMTA3, a Ca2+-regulated transcription factor, is a repressor of plant immune responses. A truncated version of CAMTA3; CAMTA3334 called N-terminal repression module (NRM), and its extended version (CAMTA447), which include the DNA binding domain, were previously reported to complement the camta3/2 mutant phenotype. Here, we generated a series of CAMTA3 truncated versions [the N-terminus (aa 1-517), C-terminus (aa 517-1032), R1 (aa 1-173), R2 (aa 174-345), R3 (aa 346-517), R4 (aa 517-689), R5 (aa 690-861) and R6 (aa 862-1032)], expressed in camta3 mutant and analyzed the phenotypes of the transgenic lines. Interestingly, unlike CAMTA447, extending the N-terminal region to 517 aa did not complement the camta3 phenotype, suggesting that the amino acid region from 448-517 (70 aa), which includes a part of the TIG domain suppresses the NRM activity. The C-terminus and other truncated versions (R1-R6) also failed to complement the camta3 mutant. Expressing the full length or NRM of CAMTA3 in camta3 plants suppressed the activation of immune-responsive genes and increased the expression of cold-induced genes. In contrast, the transgenic lines expressing the N- or C-terminus or R1-R6 of CAMTA3 showed expression patterns like those of the camta3 with enhanced expression of the defense genes and suppressed expression of the cold response genes. Furthermore, like camta3, the transgenic lines expressing the N- or C-terminus, or R1-R6 of CAMTA3 exhibited higher levels of H2O2 and increased resistance to a Pst DC3000 as compared to WT, NRM, or FL-CAMTA3 transgenic plants. Our studies identified a novel regulatory region in CAMTA3 that suppresses the NRM activity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01401-w.

DNA-Binding Activity of CAMTA3 Is Essential for Its Function: Identification of Critical Amino Acids for Its Transcriptional Activity

Calmodulin-binding transcription activators (CAMTAs), a small family of highly conserved transcription factors, function in calcium-mediated signaling pathways. Of the six CAMTAs in Arabidopsis, CAMTA3 regulates diverse biotic and abiotic stress responses. A recent study has shown that CAMTA3 is a guardee of NLRs (Nucleotide-binding, Leucine-rich repeat Receptors) in modulating plant immunity, raising the possibility that CAMTA3 transcriptional activity is dispensable for its function. Here, we show that the DNA-binding activity of CAMTA3 is essential for its role in mediating plant immune responses. Analysis of the DNA-binding (CG-1) domain of CAMTAs in plants and animals showed strong conservation of several amino acids. We mutated six conserved amino acids in the CG-1 domain to investigate their role in CAMTA3 function. Electrophoretic mobility shift assays using these mutants with a promoter of its target gene identified critical amino acid residues necessary for DNA-binding activity. In addition, transient assays showed that these residues are essential for the CAMTA3 function in activating the Rapid Stress Response Element (RSRE)-driven reporter gene expression. In line with this, transgenic lines expressing the CG-1 mutants of CAMTA3 in the camta3 mutant failed to rescue the mutant phenotype and restore the expression of CAMTA3 downstream target genes. Collectively, our results provide biochemical and genetic evidence that the transcriptional activity of CAMTA3 is indispensable for its function.

Molecular regulation of the salicylic acid hormone pathway in plants under changing environmental conditions

Salicylic acid (SA) is a central plant hormone mediating immunity, growth, and development. Recently, studies have highlighted the sensitivity of the SA pathway to changing climatic factors and the plant microbiome. Here we summarize organizing principles and themes in the regulation of SA biosynthesis, signaling, and metabolism by changing abiotic/biotic environments, focusing on molecular nodes governing SA pathway vulnerability or resilience. We especially highlight advances in the thermosensitive mechanisms underpinning SA-mediated immunity, including differential regulation of key transcription factors (e.g., CAMTAs, CBP60g, SARD1, bHLH059), selective protein-protein interactions of the SA receptor NPR1, and dynamic phase separation of the recently identified GBPL3 biomolecular condensates. Together, these nodes form a biochemical paradigm for how the external environment impinges on the SA pathway.