Small heat shock protein responses in leaf tissues of wheat cultivars with different heat susceptibility

Salinity stress improves antioxidant potential by modulating physio-biochemical responses in Moringa oleifera Lam

Moringa oleifera Lam. is a common edible plant, famous for several nutritional and therapeutic benefits. This study investigates the salt -induced modulations in plant growth, physio-biochemical responses, and antioxidant performance of M. oleifera grown under 0, 50, and 100 mM NaCl concentrations. Results showed that the plant effectively managed moderate salinity (50 mM NaCl) by maintaining succulence, weight ratios, and biomass allocation patterns of both shoot and root with minimal reduction in dry biomass. However, high salinity (100 mM NaCl) remarkably declined all growth parameters. The plant accumulated more Na⁺ and Cl^-, while less K⁺ under salinity as compared to the control. Consequently, osmotic potentials of both root and leaf decreased under salinity, which was corroborated by the high amount of proline and soluble sugars. Increased level of H₂O₂ with significantly unchanged membrane fluidity indicating its role in perceiving and managing stress at moderate salinity. In addition, increased activities of superoxide dismutase, and catalase, with increased glutathione and flavonoid contents suggest an integrated participation of both enzymatic and non-enzymatic antioxidant components in regulating ROS. On the other hand, high salinity caused an outburst of ROS indicated by high H₂O₂, MDA, and electrolyte leakage. As a response, moringa drastically increased the activities of all antioxidant enzymes and contents of antioxidant molecules including ascorbic acid, glutathione, total phenols, and flavonoids with high radical scavenging and reducing power capacities. However, a considerable amount of energy was used in such management resulting in a significant growth reduction at 100 mM NaCl. This study suggests that moringa effectively resisted moderate salinity by modulating physio-biochemical attributes and effectively managing ion toxicity and oxidative stress. Salt stress also enhanced the medicinal potentials of moringa by increasing the contents of antioxidant compounds including ascorbic acid, glutathione, total phenols, and flavonoids and their resulting activities. It can be grown on degraded/ saline lands and biomass of this plant can be used for edible and medicinal purposes, besides providing other benefits in a global climate change scenario.

Thermotolerance effect of plant growth-promoting Bacillus cereus SA1 on soybean during heat stress

BACKGROUND

Incidences of heat stress due to the changing global climate can negatively affect the growth and yield of temperature-sensitive crops such as soybean variety, Pungsannamul. Increased temperatures decrease crop productivity by affecting biochemical, physiological, molecular, and morphological factors either individually or in combination with other abiotic stresses. The application of plant growth-promoting endophytic bacteria (PGPEB) offers an ecofriendly approach for improving agriculture crop production and counteracting the negative effects of heat stress.

RESULTS

We isolated, screened and identified thermotolerant B. cereus SA1 as a bacterium that could produce biologically active metabolites, such as gibberellin, indole-3-acetic acid, and organic acids. SA1 inoculation improved the biomass, chlorophyll content, and chlorophyll fluorescence of soybean plants under normal and heat stress conditions for 5 and 10 days. Heat stress increased abscisic acid (ABA) and reduced salicylic acid (SA); however, SA1 inoculation markedly reduced ABA and increased SA. Antioxidant analysis results showed that SA1 increased the ascorbic acid peroxidase, superoxide dismutase, and glutathione contents in soybean plants. In addition, heat stress markedly decreased amino acid contents; however, they were increased with SA1 inoculation. Heat stress for 5 days increased heat shock protein (HSP) expression, and a decrease in GmHSP expression was observed after 10 days; however, SA1 inoculation augmented the heat stress response and increased HSP expression. The stress-responsive GmLAX3 and GmAKT2 were overexpressed in SA1-inoculated plants and may be associated with decreased reactive oxygen species generation, altered auxin and ABA stimuli, and enhanced potassium gradients, which are critical in plants under heat stress.

CONCLUSION

The current findings suggest that B. cereus SA1 could be used as a thermotolerant bacterium for the mitigation of heat stress damage in soybean plants and could be commercialized as a biofertilizer only in case found non-pathogenic.

Extending thermotolerance to tomato seedlings by inoculation with SA1 isolate of Bacillus cereus and comparison with exogenous humic acid application

Heat stress is one of the major abiotic stresses that impair plant growth and crop productivity. Plant growth-promoting endophytic bacteria (PGPEB) and humic acid (HA) are used as bio-stimulants and ecofriendly approaches to improve agriculture crop production and counteract the negative effects of heat stress. Current study aimed to analyze the effect of thermotolerant SA1 an isolate of Bacillus cereus and HA on tomato seedlings. The results showed that combine application of SA1+HA significantly improved the biomass and chlorophyll fluorescence of tomato plants under normal and heat stress conditions. Heat stress increased abscisic acid (ABA) and reduced salicylic acid (SA) content; however, combined application of SA1+HA markedly reduced ABA and increased SA. Antioxidant enzymes activities revealed that SA1 and HA treated plants exhibited increased levels of ascorbate peroxidase (APX), superoxide dismutase (SOD), and reduced glutathione (GSH). In addition, heat stress markedly reduced the amino acid contents; however, the amino acids were increased with co-application of SA1+HA. Similarly, inductively-coupled plasma mass-spectrometry results showed that plants treated with SA1+HA exhibited significantly higher iron (Fe+), phosphorus (P), and potassium (K+) uptake during heat stress. Heat stress increased the relative expression of SlWRKY33b and autophagy-related (SlATG5) genes, whereas co-application of SA1+HA augmented the heat stress response and reduced SlWRKY33b and SlATG5 expression. The heat stress-responsive transcription factor (SlHsfA1a) and high-affinity potassium transporter (SlHKT1) were upregulated in SA1+HA-treated plants. In conclusion, current findings suggest that co-application with SA1+HA can be used for the mitigation of heat stress damage in tomato plants and can be commercialized as a biofertilizer.

Molecular evolution and structural variations in nuclear encoded chloroplast localized heat shock protein 26 (sHSP26) from genetically diverse wheat species

Heat shock proteins are an important class of molecular chaperones known to impart tolerance under high temperature stress. sHSP26, a member of small heat shock protein subfamily is specifically involved in protecting plant's photosynthetic machinery. The present study aimed at identifying and characterizing sequence and structural variations in sHSP26 from genetically diverse progenitor and non-progenitor species of wheat. In silico analysis identified three paralogous copies of TaHSP26 to reside on short arm of chromosome 4A while one homeologue each was localized on long arm of chromosome 4B and 4D of cultivated bread wheat. Wild DD-genome donor Aegilops tauschii carried an additional sHSP26 gene (AET4Gv20569400) which was absent in the cultivated DD genome of bread wheat. In vitro amplification of this novel gene in wild accessions of Ae. tauschii and synthetic hexaploid wheat but not in cultivated bread wheat validated this finding. Further, significant length polymorphism could be identified in exon1 from diverse sHSP26 sequences. Multiple sequence alignment of procured sequences revealed numerous sSNPs and nsSNPs. D3A, P125 L, Q242 K were designated as homeolog specific- while A49 G as non-progenitor specific amino acid replacements. A 9-bp indel in TmHSP26-1(GA) translated into a deletion of SPM amino acid segment in chloroplast specific conserved consensus region III. High degree of divergence in nucleotide sequence between cultivated and wild species appeared in the form of higher ω values (Ka/Ks >1) indicating positive selection during the course of evolution. Phylogenetic analysis elucidated ancestral relationships between wheat sHSP26 proteins and orthologous proteins across plant kingdom. Overall, data mining approach may be employed as an effective pre-breeding strategy to identify and mobilize novel stress responsive genes and distinct allelic variants from wider germplasm collections of wheat to enhance climate resilience of present day elite wheat cultivars.

Genome-wide identification and analysis of biotic and abiotic stress regulation of small heat shock protein (HSP20) family genes in bread wheat

Small Heat Shock Proteins (sHSPs)/HSP20 are molecular chaperones that protect plants by preventing protein aggregation during abiotic stress conditions, especially heat stress. Due to global climate change, high temperature is emerging as a major threat to wheat productivity. Thus, the identification of HSP20 and analysis of HSP transcriptional regulation under different abiotic stresses in wheat would help in understanding the role of these proteins in abiotic stress tolerance. We used sequences of known rice and Arabidopsis HSP20 HMM profiles as queries against publicly available wheat genome and wheat full length cDNA databases (TriFLDB) to identify the respective orthologues from wheat. 163 TaHSP20 (including 109 sHSP and 54 ACD) genes were identified and classified according to the sub-cellular localization and phylogenetic relationship with sequenced grass genomes (Oryza sativa, Sorghum bicolor, Zea mays, Brachypodium distachyon and Setaria italica). Spatio-temporal, biotic and abiotic stress-specific expression patterns in normalized RNA seq and wheat array datasets revealed constitutive as well as inductive responses of HSP20 in different tissues and developmental stages of wheat. Promoter analysis of TaHSP20 genes showed the presence of tissue-specific, biotic, abiotic, light-responsive, circadian and cell cycle-responsive cis-regulatory elements. 14 TaHSP20 family genes were under the regulation of 8 TamiRNA genes. The expression levels of twelve HSP20 genes were studied under abiotic stress conditions in the drought- and heat-tolerant wheat genotype C306. Of the 13 TaHSP20 genes, TaHSP16.9H-CI showed high constitutive expression with upregulation only under salt stress. Both heat and salt stresses upregulated the expression of TaHSP17.4-CI, TaHSP17.7A-CI, TaHSP19.1-CIII, TaACD20.0B-CII and TaACD20.6C-CIV, while TaHSP23.7-MTI was specifically induced only under heat stress. Our results showed that the identified TaHSP20 genes play an important role under different abiotic stress conditions. Thus, the results illustrate the complexity of the TaHSP20 gene family and its stress regulation in wheat, and suggest that sHSPs as attractive breeding targets for improvement of the heat tolerance of wheat.

Molecular interactions between wheat and cereal aphid (Sitobion avenae): analysis of changes to the wheat proteome

Aphids are major insect pests of cereal crops, acting as virus vectors as well as causing direct damage. The responses of wheat to infestation by cereal aphid (Sitobion avenae) were investigated in a proteomic analysis. Approximately, 500 protein spots were reproducibly detected in the extracts from leaves of wheat seedlings after extraction and 2-DE. Sixty-seven spots differed significantly between control and infested plants following 24 h of aphid feeding, with 27 and 11 up-regulated, and 8 and 21 down-regulated, in local or systemic tissues, respectively. After 8 days, 80 protein spots differed significantly between control and aphid treatments with 13 and 18 up-regulated and 27 and 22 down-regulated in local or systemic tissues, respectively. As positive controls, plants were treated with salicylic acid or methyl jasmonate; 81 and 37 differentially expressed protein spots, respectively, were identified for these treatments. Approximately, 50% of differentially expressed protein spots were identified by PMF, revealing that the majority of proteins altered by aphid infestation were involved in metabolic processes and photosynthesis. Other proteins identified were involved in signal transduction, stress and defence, antioxidant activity, regulatory processes, and hormone responses. Responses to aphid attack at the proteome level were broadly similar to basal non-specific defence and stress responses in wheat, with evidence of down-regulation of insect-specific defence mechanisms, in agreement with the observed lack of aphid resistance in commercial wheat lines.