Coping with drought: stress and adaptive mechanisms, and management through cultural and molecular alternatives in cotton as vital constituents for plant stress resilience and fitness

Increased levels of greenhouse gases in the atmosphere and associated climatic variability is primarily responsible for inducing heat waves, flooding and drought stress. Among these, water scarcity is a major limitation to crop productivity. Water stress can severely reduce crop yield and both the severity and duration of the stress are critical. Water availability is a key driver for sustainable cotton production and its limitations can adversely affect physiological and biochemical processes of plants, leading towards lint yield reduction. Adaptation of crop husbandry techniques suitable for cotton crop requires a sound understanding of environmental factors, influencing cotton lint yield and fiber quality. Various defense mechanisms e.g. maintenance of membrane stability, carbon fixation rate, hormone regulation, generation of antioxidants and induction of stress proteins have been found play a vital role in plant survival under moisture stress. Plant molecular breeding plays a functional role to ascertain superior genes for important traits and can offer breeder ready markers for developing ideotypes. This review highlights drought-induced damage to cotton plants at structural, physiological and molecular levels. It also discusses the opportunities for increasing drought tolerance in cotton either through modern gene editing technology like clustered regularly interspaced short palindromic repeat (CRISPR/Cas9), zinc finger nuclease, molecular breeding as well as through crop management, such as use of appropriate fertilization, growth regulator application and soil amendments.

The antioxidative defense system is involved in the premature senescence in transgenic tobacco (Nicotiana tabacum NC89)

BACKGROUND: α-Farnesene is a volatile sesquiterpene synthesized by the plant mevalonate (MVA) pathway through the action of α-farnesene synthase. The α-farnesene synthase 1 (MdAFS1) gene was isolated from apple peel (var. white winterpearmain), and transformed into tobacco (Nicotiana tabacum NC89). The transgenic plants had faster stem elongation during vegetative growth and earlier flowering than wild type (WT). Our studies focused on the transgenic tobacco phenotype. RESULTS: The levels of chlorophyll and soluble protein decreased and a lower seed biomass and reduced net photosynthetic rate (Pn) in transgenic plants. Reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and superoxide radicals (O2._) had higher levels in transgenics compared to controls. Transgenic plants also had enhanced sensitivity to oxidative stress. The transcriptome of 8-week-old plants was studied to detect molecular changes. Differentially expressed unigene analysis showed that ubiquitin-mediated proteolysis, cell growth, and death unigenes were upregulated. Unigenes related to photosynthesis, antioxidant activity, and nitrogen metabolism were downregulated. Combined with the expression analysis of senescence marker genes, these results indicate that senescence started in the leaves of the transgenic plants at the vegetative growth stage. CONCLUSIONS: The antioxidative defense system was compromised and the accumulation of reactive oxygen species (ROS) played an important role in the premature aging of transgenic plants.

Isolation of choline monooxygenase (CMO) gene from Salicornia europaea and enhanced salt tolerance of transgenic tobacco with CMO genes.

Glycinebetaine (GB) is an osmoprotectant accumulated by certain plants in response to high salinity, drought, and cold stress. Plants synthesize GB via the pathway choline → betaine aldehyde → glycinebetaine, and the first step is catalyzed by choline monooxygenase (CMO). In the present study, by using RT-PCR and RLM-RACE, a full-length CMO cDNA (1844 bp) was cloned from a halophyte Salicornia europaea, which showed high homology to other known sequences. In order to identify its function, the ORF of CMO cDNA was inserted into binary vector PBI121 to construct the chimeric plant expression vector PBI121-CMO. Using Agrobacterium (LBA4404) mediation, the recombinant plasmid was transferred into tobacco (Nicotiana tabacum). The PCR, Southern blot and RT-PCR analysis indicated the CMO gene was integrated into the tobacco genome, as well as expressed on the level of transcription. The transgenic tobacco plants were able to survive on MS medium containing 300 mmol/L NaCl and more vigorous than those of wild type with the same concentration salt treatment. In salt-stress conditions, transgenic plants had distinctly higher chlorophyll content and betaine accumulation than that of the control, while relative electrical conductivity of transgenic plants was generally lower. The results suggested the CMO gene transformation could effectively contribute to improving tobacco salt-resistance.

Cold resistance in plants: a mystery unresolved

Herbaceous temperate plants are capable of developing freezing tolerance when they are exposed to low nonfreezing temperatures. Acquired freezing tolerance involves extensive reprogramming of gene expression and metabolism. Recent full-genome transcript profiling studies, in combination with mutational and transgenic plant analyses, have provided a snapshot of the complex transcriptional network that operates under cold stress. The changes in expression of hundreds of genes in response to cold temperatures are followed by increases in the levels of hundreds of metabolites, some of which are known to have protective effects against the damaging effects of cold stress. Genetic analysis has revealed important roles for cellular metabolic signals, and for RNA splicing, export and secondary structure unwinding, in regulating cold-responsive gene expression and chilling and freezing tolerance. These results along with many of the others summarized here further our understanding of the basic mechanisms that plants have evolved to survive freezing temperatures. In addition, the findings have potential practical applications, as freezing temperatures are a major factor limiting the geographical locations suitable for growing crop and horticultural plants and periodically account for significant losses in plant productivity. Although, great progress has been made in the field but lacunae still remain since it appears that the cold resistance is more complex than perceived and involves more than one pathway.

Effect of Bt-cotton on chrysopids, ladybird beetles and their prey: aphids and whiteflies.

The effect of Bt-cotton, i.e. genetically modified cotton that contain genes expressing delta-endotoxin, on aphid, whitefly, chrysopid and coccinellid populations was determined with a two-year field study at a cotton farm near Marble Hall, South Africa. Although Bt-cotton is lepidopteran specific, non-lepidopteran arthropod populations may be indirectly influenced by the endotoxin. Abundance of aphid, whitefly, chrysopid and coccinellid populations and predator-prey interactions were used as measures to determine possible effects on the populations under investigation. The cultivation of Bt-cotton had no effect on aphid, whitefly, chrysopid or coccinellid abundance. Positive density dependent interactions occurred between aphids and coccinellids which were not influenced by Bt-cotton. A significant relationship between whitefly and coccinellid abundance, i.e. predator-prey reaction, occurred in the control and sprayed non-Bt cotton fields but was absent from the Bt-cotton fields.

Molecular cloning and characterization of a novel mannose-binding lectin cDNA from Zantedeschia aethiopica

Using RNA extracted from Zantedeschia aethiopica young leaves and primers designed according to the conservative regions of Araceae lectins, the full-length cDNA of Z. aethiopica agglutinin (ZAA) was cloned by rapid amplification of cDNA ends (RACE). The full-length cDNA of zaa was 871 bp and contained a 417 bp open reading frame (ORF) encoding a lectin precursor of 138 amino acids. Through comparative analysis of zaa gene and its deduced amino acid sequence with those of other Araceae species, it was found that zaa encoded a precursor lectin with signal peptide. Secondary and three-dimensional structure analyses showed that ZAA had many common characters of mannose-binding lectin superfamily and ZAA was a mannose-binding lectin with three mannose-binding sites. Southern blot analysis of the genomic DNA revealed that zaa belonged to a multi-copy gene family