Characterization and abiotic stress-responsive expression analysis of SGT1 genes in Brassica oleracea

OsSGT1 promotes melatonin-ameliorated seed tolerance to chromium stress by affecting the OsABI5-OsAPX1 transcriptional module in rice

Chromium (Cr) pollution threatens plant development and growth. Application of melatonin (Mel) is emerging as an effective ally to resist stress, but how Mel ameliorates seed germination upon exposure to heavy metals is poorly understood. Here, we found (i) that seed priming with Mel considerably alleviated Cr stress during rice (Oryza sativa) seed germination and (ii) that germination performance was significantly improved in suppressor of the G2 allele of skp1 (OsSGT1) overexpression lines, while mutations of OsSGT1 and/or abscisic acid-insensitive 5 (OsABI5) noticeably abrogated such Mel-induced tolerance to Cr. Complementation assays suggested that the restored expression of OsSGT1 could not rescue the weak germination of sgt1-1abi5 under Cr stress, even upon Mel priming, but the expression of OsABI5 driven by the promoter of OsSGT1 significantly restored the Mel-ameliorated germination and the expression of ascorbate peroxidase 1 (OsAPX1) in sgt1-1abi5. Further analysis indicated that OsABI5 directly regulated the transcriptional expression of OsAPX1, whose encoding products promoted H₂ O₂ scavenging to maintain redox homeostasis, which is essential for germination. Collectively, this work demonstrates that OsSGT1 regulates OsABI5 to target OsAPX1, mediating the stimulatory effects of Mel on germination of Cr-stressed seeds, which provides a guide for the application of Mel in rice production.

Melatonin Promotes SGT1-Involved Signals to Ameliorate Drought Stress Adaption in Rice

Drought has become one of the environmental threats to agriculture and food security. Applications of melatonin (MT) serve as an effective way to alleviate drought stress, but the underlying mechanism remains poorly understood. Here, we found that foliar spray of 100-µM MT greatly mitigated the severe drought stress-induced damages in rice seedlings, including improved survival rates, enhanced antioxidant system, and adjusted osmotic balance. However, mutation of the suppressor of the G2 allele of skp1 (OsSGT1) and ABSCISIC ACID INSENSITIVE 5 (OsABI5) abolished the effects of MT. Furthermore, the upregulated expression of OsABI5 was detected in wild type (WT) under drought stress, irrespective of MT treatment, whereas OsABI5 was significantly downregulated in sgt1 and sgt1abi5 mutants. In contrast, no change of the OsSGT1 expression level was detected in abi5. Moreover, mutation of OsSGT1 and OsABI5 significantly suppressed the expression of genes associated with the antioxidant system. These results suggested that the functions of OsSGT1 in the MT-mediated alleviation of drought stress were associated with the ABI5-mediated signals. Collectively, we demonstrated that OsSGT1 was involved in the drought response of rice and that melatonin promoted SGT1-involved signals to ameliorate drought stress adaption.

Expression Analysis Reveals That Sorghum Disease Resistance Protein SbSGT1 Is Regulated by Auxin

SGT1 (suppressor of the skp1 G2 allele) is an important plant disease resistance-related protein, which plays an important role in plant resistance to pathogens and regulates signal transduction during the process of plant disease resistance. In this study, we analyzed the expression profile of SbSGT1 in sorghum under phytohormones treatment. Quantitative real-time PCR results showed that SbSGT1 was most expressed in sorghum leaves, and could respond to plant hormones such as auxin, abscisic acid, salicylic acid, and brassinolide. Subsequently, we determined the optimal soluble prokaryotic expression conditions for SbSGT1 and purified it using a protein purification system in order to evaluate its potential interactions with plant hormones. Microscale thermophoretic analysis showed that SbSGT1 exhibited significant interactions with indole-3-acetic acid (IAA), with a Kd value of 1.5934. Furthermore, the transient expression of SbSGT1 in Nicotiana benthamiana indicated that treatment with exogenous auxin could inhibit SbSGT1 expression, both at the transcriptional and translational level, demonstrating that there exists an interaction between SbSGT1 and auxin.

Genome-Wide Identification and Characterization of HSP90-RAR1-SGT1-Complex Members From Arachis Genomes and Their Responses to Biotic and Abiotic Stresses

The molecular chaperone complex HSP90-RAR1-SGT1 (HRS) plays important roles in both biotic and abiotic stress responses in plants. A previous study showed that wild peanut Arachis diogoi SGT1 (AdSGT1) could enhance disease resistance in transgenic tobacco and peanut. However, no systematic analysis of the HRS complex in Arachis has been conducted to date. In this study, a comprehensive analysis of the HRS complex were performed in Arachis. Nineteen HSP90, two RAR1 and six SGT1 genes were identified from the allotetraploid peanut Arachis hypogaea, a number close to the sum of those from the two wild diploid peanut species Arachis duranensis and Arachis ipaensis. According to phylogenetic and chromosomal location analyses, thirteen orthologous gene pairs from Arachis were identified, all of which except AhHSP90-A8, AhHSP90-B9, AdHSP90-9, and AiHSP90-9 were localized on the syntenic locus, and they shared similar exon-intron structures, conserved motifs and expression patterns. Phylogenetic analysis showed that HSP90 and RAR1 from dicot and monocot plants diverged into different clusters throughout their evolution. Chromosomal location analysis indicated that AdSGT1 (the orthologous gene of AhSGT1-B3 in this study) might provide resistance to leaf late spot disease dependent on the orthologous genes of AhHSP90-B10 and AhRAR1-B in the wild peanut A. diogoi. Several HRS genes exhibited tissue-specific expression patterns, which may reflect the sites where they perform functions. By exploring published RNA-seq data, we found that several HSP90 genes play major roles in both biotic and abiotic stress responses, especially salt and drought responses. Autoactivation assays showed that AhSGT1-B1 could not be used as bait for yeast two-hybrid (Y2H) library screening. AhRAR1 and AhSGT1 could strongly interact with each other and interact with AhHSP90-B8. The present study represents the first systematic analysis of HRS complex genes in Arachis and provides valuable information for functional analyses of HRS complex genes. This study also offers potential stress-resistant genes for peanut improvement.

Targeting salt stress coping mechanisms for stress tolerance in Brassica: A research perspective

Brassica genus comprises numerous cultivated brassica species with various economic importance. Salt stress is an overwhelming problem causing serious losses in Brassica species (e.g. B. napus, B. rapa, B. oleracea, B. juncea) growth and grain yield production by inducing ionic and ROS toxicity. Given that a significant variation exists in salt tolerance level in Brassica genus, Brassica species exhibited numerous salt tolerance mechanisms which were either overlooked or given less importance to improve and understand innate salt stress tolerance mechanism in Brassica species. In this review, we tried to highlight the importance and recent findings relating to some overlooked and potential mechanisms such as role of neurotransmitters, and role of cytosolic Ca²⁺ and ROS as signaling elements to enhance salt stress tolerance. Studies revealed that salt tolerant brassica species retained more K⁺ in leaf mesophyll which confers overall salinity tolerance in salt tolerance brassica species. Neurotransmitter such as melatonin, dopamiane and eATP regulates K⁺ and Ca²⁺ permeable ion channels and plays a very crucial role in ionic homeostasis under salinity stress in brassica. At the end, the numerous possible salt stress agronomic strategies were also discussed to mitigate the severity of the salt stress in Brassica species.

On a Cold Night: Transcriptomics of Grapevine Flower Unveils Signal Transduction and Impacted Metabolism

Low temperature is a critical environmental factor limiting plant productivity, especially in northern vineyards. To clarify the impact of this stress on grapevine flower, we used the Vitis array based on Roche-NimbleGen technology to investigate the gene expression of flowers submitted to a cold night. Our objectives were to identify modifications in the transcript levels after stress and during recovery. Consequently, our results confirmed some mechanisms known in grapes or other plants in response to cold stress, notably, (1) the pivotal role of calcium/calmodulin-mediated signaling; (2) the over-expression of sugar transporters and some genes involved in plant defense (especially in carbon metabolism), and (3) the down-regulation of genes encoding galactinol synthase (GOLS), pectate lyases, or polygalacturonases. We also identified some mechanisms not yet known to be involved in the response to cold stress, i.e., (1) the up-regulation of genes encoding G-type lectin S-receptor-like serine threonine-protein kinase, pathogen recognition receptor (PRR5), or heat-shock factors among others; (2) the down-regulation of Myeloblastosis (MYB)-related transcription factors and the Constans-like zinc finger family; and (3) the down-regulation of some genes encoding Pathogen-Related (PR)-proteins. Taken together, our results revealed interesting features and potentially valuable traits associated with stress responses in the grapevine flower. From a long-term perspective, our study provides useful starting points for future investigation.

Function of the ERFL1a Transcription Factor in Wheat Responses to Water Deficiency

The APETALA2/ethylene response factor (AP2/ERF) superfamily is involved in the responses of plants to biotic and abiotic stresses; however, the functions and mechanisms of some members of this family in plants are unclear. In our previous study, expression of TaERFL1a, a member of the AP2/ERF family, was remarkably induced in wheat seedlings suffering freezing stress. In this study, we show that its expression was rapidly upregulated in response to salt, cold, and water deficiency, suggesting roles in the responses to abiotic stresses. Further, transient barley stripe mosaic virus-induced gene silencing (BSMV-VIGS) resulted in significantly reduced tolerance to 20% PEG6000-stimulated water deficiency. Subcellular localization and transcriptional activation assays separately showed that TaERFL1a was targeted to the nucleus and possessed transcriptional activation activity. Yeast two-hybrid library screening identified six interacting proteins, and of these, the interactions between TaERFL1a and TaSGT1, and TaERFL1a and TaDAD2 proteins were further confirmed by yeast co-transformation and bimolecular fluorescent complementation (BiFC). Collectively, our results suggest that TaERFL1a is a stress-responsive transcription factor, which could be functionally related to proteins involved in the abiotic stress responses of plants.

Compositional bias coupled with selection and mutation pressure drives codon usage in Brassica campestris genes

The plant Brassica campestris includes the vegetables turnip and Chinese cabbage, important plants of economic importance. Here, we have analysed the codon usage bias of B. campestris for 116 protein coding genes. Neutrality analysis showed that B. campestris had a wide range of GC3s, and a significant correlation was observed between GC12 and GC3. Nc versus GC3s plot showed a few genes on or proximate to the expected curve, but the majority of points were found to be scattered distantly from the expected curve. Correspondence analysis on codon usage revealed that the position preference of codons on multidimensional space totally depends on the presence of A and T at synonymous third codon position. These results altogether suggest that composition bias along with selection (major) and mutation pressure (minor) affects the codon usage pattern of the protein coding genes in Brassica campestris.