Peanut annexin AhANN6 promotes heat resistance in plant and bacterial cells.

The initiation of fermentation in the yeast Saccharomyces cerevisiae is associated with a rapid drop in general stress resistance. Previously we identified a mutant which is deficient in fermentation-induced loss of stress resistance (fil1), as a partially inactivating mutant in adenylate cyclase. We have now investigated possible causes of its high stress resistance. Deletion of the TPS1 gene, encoding the first enzyme in the biosynthesis of trehalose, or the heat shock protein gene HSP104 only resulted in a minor effect on heat stress resistance compared with deletion of these genes in a wild-type background. A strain with a deletion of both genes still showed a higher stress resistance in the fil1 background compared to the corresponding wild-type background. Deletion of the transcription factor genes MSN2 and MSN4, which are required for the expression of STRE-regulated genes, resulted in a dramatic drop in heat resistance in the wild-type background but had much less effect in the fil1 mutant. The fil1 msn2Deltamsn4Delta strain remained more heat-resistant than a wild-type strain. A strain in which all four genes, TPS1, HSP104, MSN2 and MSN4, are deleted was very sensitive to heat stress and also to oxidative and salt stress. Presence of the fil1 mutation in such a strain, however, still clearly enhanced heat, oxidative and salt stress resistance. These results indicate that, in addition to trehalose, Hsp104 and the Msn2/4-controlled genes, other factors exist in S. cerevisiae that can, significantly and independently of the known factors, enhance general stress resistance. The mutants described in this work provide a tool to identify these novel components.

ABSTRACTCrop productivity depends heavily on several biotic and abiotic factors. Plant annexins are a multigene family of calcium-dependent phospholipid-binding proteins that function in response to environmental stresses and signaling during growth and development of plants. We recently isolated and characterized a Triticum durum annexin, called TdANN12, which is upregulated by different abiotic stresses. Overexpression of TdANN12 in transgenic tobacco improves stress tolerance through ROS removal. This mini-review outlines the functional characterization of plant annexin genes and suggests how these features could be exploitated to improve stress tolerance in plants. Furthermore, transgenic overexpression of plant annexin genes in crops (tobacco, tomato, rice, alfalfa, cotton, and potato) will be discussed as a promising approach to acquire abiotic and biotic stress tolerance.

On the eve of global climate change, temperature increase, is the most evident phenomenon. This temperature increase is posing severe threat for sustainable crop production in many countries across the globe in the form of heat stress. Plants respond in many ways to the prevailing high temperature environment, and several inter- and intraspecific differences are reported. Heat stress produces quite tangible changes at cell, tissue, and organ levels. Photosynthetic acclimation to heat stress, synthesis and accumulation of primary and secondary metabolites, induction of stress proteins are among the major adaptive responses to heat stress. The important genes expressed in response to heat stress include heat shock protein (hsp) genes, dehydrins (dhn), senescence-associated (sag) genes, stay-green (sgr) genes. As mechanisms of heat stress tolerance, plants display the maintenance of membrane stability, scavenging of ROS, production of enzymatic and nonenzymatic antioxidants and adjustment of compatible solutes. Plant thermotolerance can be improved by various means; major being the mass screening and morphological and biochemical markers-assisted selection, identification, and mapping of QTLs conferring heat resistance, conventional and molecular breeding, and exogenous use of osmoprotectants and stress-signaling agents. Although pretty well understood, more research efforts are required to understand novel aspects of heat tolerance including molecular cloning and characterization of genes/proteins and understanding the basis of growth improvements with seed pretreatments and plant acclimations. In this chapter, we discuss the plant responses to high temperature stress and integrated approaches, such as genetics, breeding and management options to improve the resistance in plants against heat stress.

Chapter 5 - Molecular insights into stress-responsive genes in the mitigation of environmental stresses

Morphological features of different polyploids for adaptation and molecular characterization of CC-NBS-LRR and LEA gene families in Agave L.

As a temperate-cold species, Saccharina japonica often suffers heat stress when it is transplanted to temperate and subtropical zones. Study the heat stress response and resistance mechanism of Saccharina is of great significance for understanding the acclimation to heat stress under domestication as well as for breeding new cultivars with heat stress resistance. In this study, we identified a set of heat stress-responsive miRNAs and analysed their regulation during the heat stress response. CO (control) and heat stress (HS) sRNA libraries were constructed and sequenced. Forty-nine known miRNAs and 75 novel miRNAs were identified, of which seven known and 25 novel miRNAs were expressed differentially under heat stress. Quantitative PCR of six selected miRNAs confirmed that these loci were responsive to heat stress. Thirty-nine and 712 genes were predicted to be targeted by the seven known miRNAs and 25 novel miRNAs, respectively. Gene function and pathway analyses showed that these genes probably play important roles in S. japonica heat stress tolerance. The miRNAs identified represent the first set of heat-responsive miRNAs identified from S. japonica, and their identification can help elucidate the heat stress response and resistance mechanisms in S. japonica.

Plant responses and adaptations to a changing climate.

Warming climatic conditions can pose problems for crop production in many parts of the world, but detailed information on the expression of heat and drought stress resistance genes of potentially affected crop plants is lacking. This information is important to have in order to most efficiently guide the breeding of crops that are adapted to new climatic conditions. A maize (Zea mays) gene microarray, a method used worldwide to evaluate the expression of tens of thousands of genes at once, was used to investigate changes in expression of genes involved in resistance to heat and water stress in milk stage popcorn kernels from undamaged and insect-damaged ears. Popcorn is a form of maize that is more susceptible to heat and drought stress due to its smaller root system. In years of heat and drought stress, expression of many heat shock- and senescence-related proteins increased compared to the year when weather was closer to average conditions, but the expression of many genes related to drought stress resistance decreased in years of weather stress. A different complex of heat shock protein and water stress resistance protein genes had higher expression in kernels from undamaged compared to insect-damaged ears in years of heat and drought stress. These results indicate that the interaction of biotic components, such as insects, are important to consider in developing crop lines with adaptation to stress as this will help identify additional genes and their regulatory components involved in heat and drought stress resistance that might otherwise be overlooked, and will likely be an important strategy for the most effective development of climate stress-tolerant crops globally.

The Temperature Resistance of Alaskan Plants from the Continental Boreal Zone

Abiotic Stresses

Abscisic acid (ABA) concentration in wheat (Triticum aestivum L.) plants increases during heat and drought stress and is associated with stomatal closure, low photosynthetic rate, and senescence. This research was conducted to determine if wheat somaclones selected in vitro for ABA insensitivity are resistant to heat and drought stress and to identify traits that contribute to stress resistance as ABA insensitivity is increased. Five ABA‐insensitive somadones and their parental line ND7532 were grown in Hoagland's solution until anthesis, then heat and osmotic stresses were applied through maturity. Heat stress was induced by increasing temperature from 25/20 to 35/25 °C, and osmotic stress (−0.05 MPa) was induced by adding 100 g kg−1 polyethylene glycol‐1000 (PEG‐1000) to the hydroponic solution. An exceptional somaclone KTC86211 and parent ND7532 were grown in 1:1:1 sand: Reading silt loam (fine, mixed, mesic Typic Argiudoil):peat. Heat stress was applied as in the first experiment, and drought stress (−0.5 MPa) was induced by withholding water after anthesis and soil water potential was monitored with a thermocouple psychrometer. The ABA‐insensitive somaclones KTC86211 and KTC86424 had significantly lower stomatal resistance, higher variable leaf chlorophyll fluorescence, longer leaf area duration, and greater kernel wt. and grain yield per plant than the parent in the first experiment. Crop growth rate, grain filling rate, and grain filling duration were higher in the ABA‐insensitive somaclone KTC86211 than in ND7532 in the second experiment, indicating that greater grain yield per plant resulted from rapid assimilation and translocation of nutrients and delayed senescence. We concluded that ABA‐insensitive genotypes may have high growth rates and long leaf area duration under stress and that selection for ABA insensitivity may be an effective approach to improving heat and drought resistance in wheat.

BOOK REVIEW article Front. Plant Sci., 17 June 2015Sec. Plant Physiology Volume 6 - 2015 | https://doi.org/10.3389/fpls.2015.00452

Genomic and transcriptomic studies on date palm (Phoenix dactylifera) are still inadequate, but several studies have contributed to understanding its genetic makeup, especially in the Khalas cultivar. Looking at the extensive importance of WRKY transcription factors (TFs) in plant growth, development and defense responses to various biotic and abiotic stresses, we conducted a study to identify and functionally annotate the WRKY TFs of P. dactylifera, with a particular focus on their involvement in drought and heat stress. A total of 73 PdWRKY TFs were curated and classified into 7 and 17 clades through comparative phylogenetic analysis and orthologous comparison of the WRKY TFs from the extensively studied genomes of Arabidopsis thaliana and Oryza sativa, respectively. Our findings show that 52% of PdWRKYs have strong homology with OsWRKYs, while only 9 PdWRKYs have orthologous relationships with AtWRKYs. This indicates a divergence in evolutionary patterns, likely due to gene duplications and losses in rice, Arabidopsis, and date palm, that occurred both before and after the last common ancestor of these species. Our comprehensive analysis of gene structures, conserved motifs, and protein-protein interactions confirmed functional similarities among many PdWRKYs. The GO and KEGG pathway enrichment analyses validate that PdWRKY genes have significant functional roles in various molecular, cellular, and biological processes. The transcriptomics analysis revealed that heat stress resulted in upregulating 7 genes (12.2%) and downregulating 10 PdWRKY genes (17.5%). With combined drought and heat stress, 15 genes (26.3%) were upregulated, and 9 genes (15.78%) were downregulated. Notably PdWRKYs genes such as LOC103723396 (WRKY35) and LOC103718774 (WRKY1) showed significantly higher while LOC103713231(WRKY28), LOC103721327(WRKY72, LOC103721580 (WRKY50), LOC120110335 (WRKY70), and LOC103707788 (WRKY71) showed significantly lower expression under drought and heat stress conditions compared to control plants, indicating their vital role in adaptation and tolerance mechanisms against these environmental stresses. The current study will highlight the essential role of comprehensive genomic and transcriptomic studies for developing innovative approaches to promote plant growth in adverse conditions. Further studies on these PdWRKY genes could provide insights into their specific roles and mechanisms in stress response pathways in date palms, potentially leading to strategies for improving stress resilience in this important crop species.

Drought (water deficits) and heat (high temperatures) stress are the prime abiotic constraints, under the current and climate change scenario in future. Any further increase in the occurrence, and extremity of these stresses, either individually or in combination, would severely reduce the crop productivity and food security, globally. Although, they obstruct productivity at all crop growth stages, the extent of damage at reproductive phase of crop growth, mainly the seed filling phase, is critical and causes considerable yield losses. Drought and heat stress substantially affect the seed yields by reducing seed size and number, eventually affecting the commercial trait ‘100 seed weight’ and seed quality. Seed filling is influenced by various metabolic processes occurring in the leaves, especially production and translocation of photoassimilates, importing precursors for biosynthesis of seed reserves, minerals and other functional constituents. These processes are highly sensitive to drought and heat, due to involvement of array of diverse enzymes and transporters, located in the leaves and seeds. We highlight here the findings in various food crops showing how their seed composition is drastically impacted at various cellular levels due to drought and heat stresses, applied separately, or in combination. The combined stresses are extremely detrimental for seed yield and its quality, and thus need more attention. Understanding the precise target sites regulating seed filling events in leaves and seeds, and how they are affected by abiotic stresses, is imperative to enhance the seed quality. It is vital to know the physiological, biochemical and genetic mechanisms, which govern the various seed filling events under stress environments, to devise strategies to improve stress tolerance. Converging modern advances in physiology, biochemistry and biotechnology, especially the “omics” technologies might provide a strong impetus to research on this aspect. Such application, along with effective agronomic management system would pave the way in developing crop genotypes/varieties with improved productivity under drought and/or heat stresses.

High temperature inhibits wheat grain filling. Polyamines (PAs) are closely associated with plant resistance caused by abiotic stress. However, little is known about the effect of PAs on the grain filling of wheat under heat stress. Two wheat varieties differing in heat resistance were used, and endogenous PAs levels were measured during grain filling under normal growth conditions outside the greenhouse (CK), artificially simulated high temperature (HT), artificially simulated high temperature plus exogenous application of spermine (HT + Spm) and artificially simulated high temperature plus spermidine (HT + Spd) treatments. Additionally, the variation of antioxidant enzymatic activities and osmotic adjustable substances content in grains was measured during grain filling. The results showed that compared with HT,HT + Spm and HT + Spd significantly increased grain weight of XC 6 (heat-resistant variety) by 19% and 5%, and XC 31 (heat-sensitive variety) by 31% and 34%, activity of superoxide dismutase (SOD), peroxidase (POD)and catalase (CAT) and content of Spm, Spd, and proline (Pro) increased significantly, while putrescine (Put), malondialdehyde (MDA) and soluble sugar (SS)contentdecreased during grain filling; The correlation analysis showed that grain weight was negatively correlated with the content of PUT, MDA, Pro and activity of SOD and CAT and positively correlated with the content of Spd and activity of POD in grains. Our results indicated that exogenous Spm and Spd could alleviate the heat injury of grain filling.