A stress-associated protein OsSAP8 modulates gibberellic acid biosynthesis by reducing the promotive effect of transcription factor OsbZIP58 on OsKO2

Research progress on plant stress-associated protein (SAP) family: Master regulators to deal with environmental stresses

Every year, unfavorable environmental factors significantly affect crop productivity and threaten food security. Plants are sessile; they cannot move to escape unfavorable environmental conditions, and therefore, they activate a variety of defense pathways. Among them are processes regulated by stress-associated proteins (SAPs). SAPs have a specific zinc finger domain (A20) at the N-terminus and either AN1 or C2H2 at the C-terminus. SAP proteins are involved in many biological processes and in response to various abiotic or biotic constraints. Most SAPs play a role in conferring transgenic stress resistance and are stress-inducible. The emerging field of SAPs in abiotic or biotic stress response regulation has attracted the attention of researchers. Although SAPs interact with various proteins to perform their functions, the exact mechanisms of these interactions remain incompletely understood. This review aims to provide a comprehensive understanding of SAPs, covering their diversity, structure, expression, and subcellular localization. SAPs play a pivotal role in enabling crosstalk between abiotic and biotic stress signaling pathways, making them essential for developing stress-tolerant crops without yield penalties. Collectively, understanding the complex regulation of SAPs in stress responses can contribute to enhancing tolerance against various environmental stresses through several techniques such as transgenesis, classical breeding, or gene editing.

Pepper RING-Type E3 Ligase CaFIRF1 Negatively Regulates the Protein Stability of Pepper Stress-Associated Protein, CaSAP14, in the Dehydration Stress Response

As part of the cellular stress response in plants, the ubiquitin-proteasome system (UPS) plays a crucial role in regulating the protein stability of stress-related transcription factors. Previous study has indicated that CaSAP14 is functionally involved in enhancing pepper plant tolerance to dehydration stress by modulating the expression of downstream genes. However, the comprehensive regulatory mechanism underlying CaSAP14 remains incompletely understood. Here, we identified a RING-type E3 ligase, CaFIRF1, which interacts with and ubiquitinates CaSAP14. Pepper plants with silenced CaFIRF1 exhibited a dehydration-tolerant phenotype when subjected to dehydration stress, while overexpression of CaFIRF1 in pepper and Arabidopsis resulted in reduced dehydration tolerance. Co-silencing of CaFIRF1 and CaSAP14 in pepper increased sensitivity to dehydration, suggesting that CaFIRF1 acts upstream of CaSAP14. A cell-free degradation analysis demonstrated that silencing of CaFIRF1 led to decreased CaSAP14 protein degradation, implicating CaFIRF1 in the regulation of CaSAP14 protein via the 26S proteasomal degradation pathway. Our findings suggest a mechanism by which CaFIRF1 mediates the ubiquitin-dependent proteasomal degradation of CaSAP14, thereby influencing the response of pepper plants to dehydration stress.

Genome-Wide Identification of GmSPS Gene Family in Soybean and Expression Analysis in Response to Cold Stress

Sucrose metabolism plays a critical role in development, stress response, and yield formation of plants. Sucrose phosphate synthase (SPS) is the key rate-limiting enzyme in the sucrose synthesis pathway. To date, genome-wide survey and comprehensive analysis of the SPS gene family in soybean (Glycine max) have yet to be performed. In this study, seven genes encoding SPS were identified in soybean genome. The structural characteristics, phylogenetics, tissue expression patterns, and cold stress response of these GmSPSs were investigated. A comparative phylogenetic analysis of SPS proteins in soybean, Medicago truncatula, Medicago sativa, Lotus japonicus, Arabidopsis, and rice revealed four families. GmSPSs were clustered into three families from A to C, and have undergone five segmental duplication events under purifying selection. All GmSPS genes had various expression patterns in different tissues, and family A members GmSPS13/17 were highly expressed in nodules. Remarkably, all GmSPS promoters contain multiple low-temperature-responsive elements such as potential binding sites of inducer of CBF expression 1 (ICE1), the central regulator in cold response. qRT-PCR proved that these GmSPS genes, especially GmSPS8/18, were induced by cold treatment in soybean leaves, and the expression pattern of GmICE1 under cold treatment was similar to that of GmSPS8/18. Further transient expression analysis in Nicotiana benthamiana and electrophoretic mobility shift assay (EMSA) indicated that GmSPS8 and GmSPS18 transcriptions were directly activated by GmICE1. Taken together, our findings may aid in future efforts to clarify the potential roles of GmSPS genes in response to cold stress in soybean.

SlZF3 regulates tomato plant height by directly repressing SlGA20ox4 in the gibberellic acid biosynthesis pathway

Plant height is an important target trait for crop genetic improvement. Our previous work has identified a salt-tolerant C2H2 zinc finger, SlZF3, and its overexpression lines also showed a semi-dwarf phenotype, but the molecular mechanism remains to be elucidated. Here, we characterized the dwarf phenotype in detail. The dwarfism is caused by a decrease in stem internode cell elongation and deficiency of bioactive gibberellic acids (GAs), and can be rescued by exogenous GA3 treatment. Gene expression assays detected reduced expression of genes in the GA biosynthesis pathway of the overexpression lines, including SlGA20ox4. Several protein-DNA interaction methods confirmed that SlZF3 can directly bind to the SlGA20ox4 promoter and inhibit its expression, and the interaction can also occur for SlKS and SlKO. Overexpression of SlGA20ox4 in the SlZF3-overexpressing line can recover the dwarf phenotype. Therefore, SlZF3 regulates plant height by directly repressing genes in the tomato GA biosynthesis pathway.

Pepper stress-associated protein 14 is a substrate of CaSnRK2.6 that positively modulates abscisic acid-dependent osmotic stress responses

The phytohormone abscisic acid (ABA) plays a prominent role in various abiotic stress responses of plants. In the ABA-dependent osmotic stress response, SnRK2.6, one of the subclass III SnRK2 kinases, has been identified as playing a key role by phosphorylating and activating downstream genes. Although several modulatory proteins have been reported to be phosphorylated by SnRK2.6, the identities of the full spectrum of downstream targets have yet to be sufficiently established. In this study, we identified CaSAP14, a stress-associated protein in pepper (Capsicum annuum), as a downstream target of CaSnRK2.6. We elucidated the physical interaction between SnRK2.6 and CaSAP14, both in vitro and in vivo, and accordingly identified a C-terminal C2H2-type zinc finger domain of CaSAP14 as being important for their interaction. CaSAP14-silenced pepper plants showed dehydration- and high salt-sensitive phenotypes, whereas overexpression of CaSAP14 in Arabidopsis conferred tolerance to dehydration, high salinity, and mannitol treatment, with plants showing ABA-hypersensitive phenotypes. Furthermore, an in-gel kinase assay revealed that CaSnRK2.6 phosphorylates CaSAP14 in response to exogenous ABA, dehydration, and high-salinity stress. Collectively, these findings suggest that CaSAP14 is a direct substrate of CaSnRK2.6 and positively modulates dehydration- and high salinity-induced osmotic stress responses.

Identification and Analysis of Stress-Associated Proteins (SAPs) Protein Family and Drought Tolerance of ZmSAP8 in Transgenic Arabidopsis

Stress-associated proteins (SAPs), a class of A20/AN1 zinc finger proteins, play vital roles in plant stress response. However, investigation of SAPs in maize has been very limited. Herein, to better trace the evolutionary history of SAPs in maize and plants, 415 SAPs were identified in 33 plant species and four species of other kingdoms. Moreover, gene duplication mode exploration showed whole genome duplication contributed largely to SAP gene expansion in angiosperms. Phylogeny reconstruction was performed with all identified SAPs by the maximum likelihood (ML) method and the SAPs were divided into five clades. SAPs within the same clades showed conserved domain composition. Focusing on maize, nine ZmSAPs were identified. Further promoter cis-elements and stress-induced expression pattern analysis of ZmSAPs indicated that ZmSAP8 was a promising candidate in response to drought stress, which was the only AN1-AN1-C2H2-C2H2 type SAP in maize and belonged to clade I. Additionally, ZmSAP8 was located in the nucleus and had no transactivation activity in yeast. Overexpressing ZmSAP8 enhanced the tolerance to drought stress in Arabidopsis thaliana, with higher seed germination and longer root length. Our results should benefit the further functional characterization of ZmSAPs.

Negative Interactions Balance Growth and Defense in Plants Confronted with Herbivores or Pathogens

Plants have evolved a series of defensive mechanisms against pathogens and herbivores, but the defense response always leads to decreases in growth or reproduction, which has serious implications for agricultural production. Growth and defense are negatively regulated not only through metabolic consumption but also through the antagonism of different phytohormones, such as jasmonic acid (JA) and salicylic acid (SA). Meanwhile, plants can limit the expression of defensive metabolites to reduce the costs of defense by producing constitutive defenses such as glandular trichomes or latex and accumulating specific metabolites, determining the activation of plant defense or the maintenance of plant growth. Interestingly, plant defense pathways might be prepared in advance which may be transmitted to descendants. Plants can also use external organisms to protect themselves, thus minimizing the costs of defense. In addition, plant relatives exhibit cooperation to deal with pathogens and herbivores, which is also a way to regulate growth and defense.