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.

Knockdown of PagSAP11 Confers Drought Resistance and Promotes Lateral Shoot Growth in Hybrid Poplar (Populus alba × Populus tremula var. glandulosa)

Plants have evolved defense mechanisms to overcome unfavorable climatic conditions. The growth and development of plants are regulated in response to environmental stress. In this study, we investigated the molecular and physiological characteristics of a novel gene PagSAP11 in hybrid poplar (Populus alba × Populus tremula var. glandulosa) under drought stress. PagSAP11, a stress-associated protein (SAP) family gene, encodes a putative protein containing an A20 and AN1 zinc-finger domain at its N- and C-termini, respectively. Knockdown of PagSAP11 transgenic poplars (SAP11-Ri) enhanced their tolerance to drought stress compared with wild type plants. Moreover, the RNAi lines showed increased branching of lateral shoots that led to a gain in fresh weight, even when grown in the living modified organism (LMO) field. In SAP11-Ri transgenic plants, the expression levels of genes involved in axillary bud outgrowth and cell proliferation such as DML10, CYP707A and RAX were increased while the DRM gene which involved in bud dormancy was down-regulated. Taken together, these results indicate that PagSAP11 represents a promising candidate gene for engineering trees with improved stress tolerance and growth during unfavorable conditions.

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

Gibberellic acid (GA) is a vital phytohormone for plant growth and development. GA biosynthesis is a complex pathway regulated by various transcription factors. Here we report a stress-associated protein 8 (OsSAP8), negatively involved in GA biosynthesis. Overexpression of OsSAP8 in rice resulted in a semi-dwarfism phenotype and reduced endogenous GA3 content. In contrast, an OsSAP8 knockout mutant exhibited higher endogenous GA3 content and slightly increased plant height. Sub-cellular localization analysis of OsSAP8 showed that it could enter the nucleus. Based on electrophoretic mobility shift assay and yeast one hybrid experiments, OsSAP8 was found to bind to the cis-acting regulatory element GADOWNAT of ent-kaurene oxidases (KO2, KO3, KO5). The results from dual-luciferase reporter assays showed that OsSAP8 does not activate LUC reporter gene expression. However, it could interact with basic leucine zipper 58 (OsbZIP58), which has strong transcriptional activation potential on OsKO2. Moreover, the interaction between OsSAP8, rice lesion simulating disease 1-like 1 (OsLOL1), and OsbZIP58 could reduce the promotive effect of transcription factor OsbZIP58 on OsKO2. These results provide some new insights on the regulation of GA biosynthesis in rice.

Stress associated proteins coordinate the activation of comprehensive antiviral immunity in Phalaenopsis orchids

Viruses cause severe damage on crops, and identification of key gene(s) that can comprehensively activate antiviral immunity will provide insights for designing effective antiviral strategies. Salicylic acid (SA)-mediated antiviral immunity and RNA interference (RNAi) are two independently discovered antiviral pathways. Previously, we identified the orchid stress-associated protein (SAP), Pha13, which serves as a hub in SA-mediated antiviral immunity. As SAPs exist as a protein family, whether duplicated SAPs have redundant or distinctive functions in antiviral immunity remains elusive. We performed functional assays on orchid Pha21, a homolog of Pha13, using transient and transgenic approaches on orchid, Arabidopsis and Nicotiana benthamiana to overexpress and/or silence Pha21. The SA treatment induced the expression of both Pha13 and Pha21, whereas Pha21 was found to play a key role in the initiation of the RNAi pathway in Phalaenopsis orchids. We demonstrated that Pha21-mediated antiviral immunity and enhancement of the RNAi pathway is conserved between dicotyledons and monocotyledons. We provide new insight that orchid SAPs confer distinctive functions to coordinate both SA-signaling and RNAi for comprehensive activation of antiviral immunity, and this information will help us develop antiviral strategies on crops.

Identification of DHX36 as a tumour suppressor through modulating the activities of the stress-associated proteins and cyclin-dependent kinases in breast cancer

The nucleic acid guanine-quadruplex structures (G4s) are involved in many aspects of cancer progression. The DEAH-box polypeptide 36 (DHX36) has been identified as a dominant nucleic acid helicase which targets and disrupts DNA and RNA G4s in an ATP-dependent manner. However, the actual role of DHX36 in breast cancer remains unknown. In this study, we observed that the gene expression of DHX36 was positively associated with patient survival in breast cancer. The abundance of DHX36 is also linked with pathologic conditions and the stage of breast cancer. By using the xenograft mouse model, we demonstrated that the stable knockdown of DHX36 via lentivirus in breast cancer cells significantly promoted tumour growth. We also found that, after the DHX36 knockdown (KD), the invasion of triple-negative breast cancer cells was enhanced. In addition, we found a significant increase in the number of cells in the S-phase and a reduction of apoptosis with the response to cisplatin. DHX36 KD also desensitized the cytotoxic cellular response to paclitaxel and cisplatin. Transcriptomic profiling analysis by RNA sequencing indicated that DHX36 altered gene expression profile through the upstream activation of TNF, IFNγ, NFκb and TGFβ1. High throughput signalling analysis showed that one cluster of stress-associated kinase proteins including p53, ROCK1 and JNK were suppressed, while the mitotic checkpoint protein-serine kinases CDK1 and CDK2 were activated, as a consequence of the DHX36 knockdown. Our study reveals that DHX36 functions as a tumour suppressor and may be considered as a potential therapeutic target in breast cancer.

A Stress-Associated Protein, PtSAP13, From Populus trichocarpa Provides Tolerance to Salt Stress

The growth and production of poplars are usually affected by unfavorable environmental conditions such as soil salinization. Thus, enhancing salt tolerance of poplars will promote their better adaptation to environmental stresses and improve their biomass production. Stress-associated proteins (SAPs) are a novel class of A20/AN1 zinc finger proteins that have been shown to confer plants' tolerance to multiple abiotic stresses. However, the precise functions of SAP genes in poplars are still largely unknown. Here, the expression profiles of Populus trichocarpa SAPs in response to salt stress revealed that PtSAP13 with two AN1 domains was up-regulated dramatically during salt treatment. The β-glucuronidase (GUS) staining showed that PtSAP13 was accumulated dominantly in leaf and root, and the GUS signal was increased under salt condition. The Arabidopsis transgenic plants overexpressing PtSAP13 exhibited higher seed germination and better growth than wild-type (WT) plants under salt stress, demonstrating that overexpression of PtSAP13 increased salt tolerance. Higher activities of antioxidant enzymes were found in PtSAP13-overexpressing plants than in WT plants under salt stress. Transcriptome analysis revealed that some stress-related genes, including Glutathione peroxidase 8, NADP-malic enzyme 2, Response to ABA and Salt 1, WRKYs, Glutathione S-Transferase, and MYBs, were induced by salt in transgenic plants. Moreover, the pathways of flavonoid biosynthesis and metabolic processes, regulation of response to stress, response to ethylene, dioxygenase activity, glucosyltransferase activity, monooxygenase activity, and oxidoreductase activity were specially enriched in transgenic plants under salt condition. Taken together, our results demonstrate that PtSAP13 enhances salt tolerance through up-regulating the expression of stress-related genes and mediating multiple biological pathways.