Tolerance to environmental stresses:Do fungal endophytes mediate plasticity in <i>Solanum dulcamara</i>?

Salinity imposes constraints on plant growth and development. Efforts have been made to develop salt-tolerant crops by different methods, the outcomes have not yet been sufficiently satisfactory. Plants depend on their symbiotic partners such as fungal symbionts to cope with stress conditions such as salinity. Bittersweet nightshade (Solanum dulcamara) has a wide ecological amplitude. Although S. dulcamara is becoming a model plant species, its associated fungal symbionts have hardly been studied. Here we propose that its symbiotic, endophytic fungi may be responsible for S. dulcamara's wide ecological amplitude. We examined the composition of endophytic fungal communities in S. dulcamara from contrasting habitats, i.e., dry and wet regions. We developed a method to select potential isolates based on their ability to colonize, grow and impart tolerance under stress conditions. The isolates identified from this study could potentially be used to improve crop productivity under suboptimal conditions

Is Endophytic Colonization of Host Plants a Method of Alleviating Drought Stress?: Conceptualizing the Hidden World of Endophytes

In the wake of changing climatic conditions, plants are frequently exposed to a wide range of biotic and abiotic stresses at various stages of their development, all of which negatively affect their growth, development, and productivity. Drought is one of the most devastating abiotic stresses for most cultivated crops, particularly in arid and semiarid environments. Conventional breeding and biotechnological approaches are used to generate drought-tolerant crop plants. However, these techniques are costly and time-consuming. Plant-colonizing microbes, notably, endophytic fungi, have received increasing attention in recent years since they can boost plant growth and yield and can strengthen plant responses to abiotic stress. In this review, we describe these microorganisms and their relationship with host plants, summarize the current knowledge on how they “reprogram” the plants to promote their growth, productivity, and drought tolerance, and explain why they are promising agents in modern agriculture

Leaf Cuticular Wax, a Trait for Multiple Stress Resistance in Crop Plants

Cuticular waxes form the primary interface between a plant and its external environment. The most important function of this hydrophobic interface is regulation of non-stomatal water loss, gas exchange and conferring resistance to a wide range of biotic as well as abiotic stresses. The biosynthesis, transport and deposition of the cuticular waxes are tightly coordinated by complex molecular networks, which are also often regulated in response to various developmental, biotic as well as abiotic cues. Evidences from model as well as non-model systems suggest that targeted manipulation of the molecular regulators of wax biosynthetic pathways could enhance plant resistance to multiple stresses as well as enhance the post-harvest quality of produce. Under the current scenario of varying climatic conditions, where plants often encounter multiple stress conditions, cuticular waxes is an appropriate trait to be considered for crop improvement programs, as any attempt to improve cuticular traits would be advantageous to the crop to enhance its adaptability to diverse adverse conditions. This chapter briefs on the significance of cuticular waxes in plants, its biosynthesis, transport and deposition, its implication on plant resistance to adverse conditions, and the current options in targeted manipulation of wax-traits for breeding new crop types

Expression of Multiple Resistance Genes Enhances Tolerance to Environmental Stressors in Transgenic Poplar (Populus × euramericana ‘Guariento’)

Commercial and non-commercial plants face a variety of environmental stressors that often cannot be controlled. In this study, transgenic hybrid poplar (Populus × euramericana ‘Guariento’) harboring five effector genes (vgb, SacB, JERF36, BtCry3A and OC-I) were subjected to drought, salinity, waterlogging and insect stressors in greenhouse or laboratory conditions. Field trials were also conducted to investigate long-term effects of transgenic trees on insects and salt tolerance in the transformants. In greenhouse studies, two transgenic lines D5-20 and D5-21 showed improved growth, as evidenced by greater height and basal diameter increments and total biomass relative to the control plants after drought or salt stress treatments. The improved tolerance to drought and salt was primarily attributed to greater instantaneous water use efficiency (WUEi) in the transgenic trees. The chlorophyll concentrations tended to be higher in the transgenic lines under drought or saline conditions. Transformed trees in drought conditions accumulated more fructan and proline and had increased Fv/Fm ratios (maximum quantum yield of photosystem II) under waterlogging stress. Insect-feeding assays in the laboratory revealed a higher total mortality rate and lower exuviation index of leaf beetle [Plagiodera versicolora (Laicharting)] larvae fed with D5-21 leaves, suggesting enhanced insect resistance in the transgenic poplar. In field trials, the dominance of targeted insects on 2-year-old D5-21 transgenic trees was substantially lower than that of the controls, indicating enhanced resistance to Coleoptera. The average height and DBH (diameter at breast height) of 2.5-year-old transgenic trees growing in naturally saline soil were 3.80% and 4.12% greater than those of the control trees, but these increases were not significant. These results suggested that multiple stress-resistance properties in important crop tree species could be simultaneously improved, although additional research is needed to fully understand the relationships between the altered phenotypes and the function of each transgene in multigene transformants

Root mediated uptake of Salmonella is different from phyto-pathogen and associated with the colonization of edible organs

BackgroundPre-harvest contamination of fruits and vegetables by Salmonella in fields is one of the causes of food-borne outbreaks. Natural openings like stomata, hydathodes and fruit cracks are known to serve as entry points. While there are reports indicating that Salmonella colonize and enter root through lateral root emerging area, further investigations regarding how the accessibility of Salmonella to lateral root is different from phyto-pathogenic bacteria, the efficacy of lateral root to facilitate entry have remained unexplored. In this study we attempted to investigate the lateral root mediated entry of Salmonella, and to bridge this gap in knowledge.ResultsUnlike phytopathogens, Salmonella cannot utilize cellulose as the sole carbon source. This negates the fact of active entry by degrading plant cellulose and pectin. Endophytic Salmonella colonization showed a high correlation with number of lateral roots. When given equal opportunity to colonize the plants with high or low lateral roots, Salmonella internalization was found higher in the plants with more lateral roots. However, the epiphytic colonization in both these plants remained unaltered. To understand the ecological significance, we induced lateral root production by increasing soil salinity which made the plants susceptible to Salmonella invasion and the plants showed higher Salmonella burden in the aerial organs.ConclusionSalmonella, being unable to degrade plant cell wall material relies heavily on natural openings. Therefore, its invasion is highly dependent on the number of lateral roots which provides an entry point because of the epidermis remodeling. Thus, when number of lateral root was enhanced by increasing the soil salinity, plants became susceptible to Salmonella invasion in roots and its transmission to aerial organs

Down-regulation of an abiotic stress related <i>Nicotiana benthamiana</i> WRKY transcription factor induces physiological abnormalities

53-60Transcription factors (TFs), the DNA binding proteins, play key role in biotic and abiotic stress responses in plants by regulating the expression of downstream target genes. Many different TFs have been cloned and characterized in model plants and a few of them have been shown to have direct role in abiotic stress tolerance. In the present report, we have cloned a partial cDNA of AtWRKY75 like gene (NbWRKY) from the model plant, Nicotiana benthamiana, and studied its expression under whole plant desiccation (drought) stress. To induce drought stress, soil water status (field capacity, FC) was maintained between 60-65% by controlled irrigation and replacing water transpired twice a day. The extent of drought stress was assessed by monitoring the leaf water status and quantifying photosynthetic pigments. The semi-quantitative RT-PCR revealed constitutive expression of NbWRKY and up-regulation under drought. Down-regulation of NbWRKY by virus induced gene silencing (VIGS) produced chlorosis and senescing phenotype in N. benthamiana. The silenced plants showed reduced photosynthesis, efficiency of open PSII reaction centre, and exhibited the symptoms of photoinhibition. The results indicated the indispensable role of NbWRKY in basic physiological processes

Activation of drought tolerant traits in crops: endophytes as elicitors

Drought challenges crop production worldwide. The issue is aggravated by frequent drought episodes and unpredictable rainfall patterns associated with global climate change. While the efforts to breed drought-resistant crop varieties are progressing, the need of the hour is immediate strategies to sustain the yields of existing ones. As per recent studies, stress adaptive traits can be activated using specific elicitors. Endophytes that inhabit host plants asymptomatically are natural elicitors/bio-stimulators capable of activating host gene expression, conferring several benefits to the hosts. This review discusses the scope of using trait-specific endophytes in activating drought adaptive traits in crop varieties

Expression of <i>AtDREB2A</i>, <i>AtHB7</i> and <i>AtABF3</i> target genes in wild type and transgenic plants under drought stress condition.

<p>The transcript levels of nine downstream genes were determined by RT-PCR in drought stressed wild type (WT) and transgenic lines (L1 & L7). The, eukaryotic elongation factor (<i>ELF-A</i>) was used as internal control. The downstream genes used for expression studies were <i>AhProline amino peptidase</i> like protein; <i>AhRing box protein1</i> (<i>AhRbx1</i>); <i>Late embryogenesis abundant 4</i> (<i>AhLEA4</i>); <i>AhGlutaredoxin</i> like protein; <i>AhAldehyde reductase</i> (<i>AhAR</i>) like protein; <i>AhSerine threonine kinase</i> like protein; <i>Heat shock Protein70</i> (<i>AhHSP70</i>); <i>AhCalmodulin</i> like protein; <i>Dehydration inducible protein</i> (<i>AhDIP</i>).</p

Simultaneous Expression of Abiotic Stress Responsive Transcription Factors, <i>AtDREB2A, AtHB7</i> and <i>AtABF3</i> Improves Salinity and Drought Tolerance in Peanut (<i>Arachis hypogaea</i> L.)

<div><p>Drought, salinity and extreme temperatures are the most common abiotic stresses, adversely affecting plant growth and productivity. Exposure of plants to stress activates stress signalling pathways that induce biochemical and physiological changes essential for stress acclimation. Stress tolerance is governed by multiple traits, and importance of a few traits in imparting tolerance has been demonstrated. Under drought, traits linked to water mining and water conservation, water use efficiency and cellular tolerance (CT) to desiccation are considered to be relevant. In this study, an attempt has been made to improve CT in drought hardy crop, peanut (<i>Arachis hypogaea</i> L., <i>cv.</i> TMV2) by co-expressing stress-responsive transcription factors (TFs), <i>AtDREB2A, AtHB7</i> and <i>AtABF3</i>, associated with downstream gene expression. Transgenic plants simultaneously expressing these TFs showed increased tolerance to drought, salinity and oxidative stresses compared to wild type, with an increase in total plant biomass. The transgenic plants exhibited improved membrane and chlorophyll stability due to enhanced reactive oxygen species scavenging and osmotic adjustment by proline synthesis under stress. The improvement in stress tolerance in transgenic lines were associated with induced expression of various CT related genes like <i>AhGlutaredoxin</i>, <i>AhAldehyde reductase</i>, <i>AhSerine threonine kinase</i> like protein, <i>AhRbx1</i>, <i>AhProline amino peptidase</i>, <i>AhHSP70</i>, <i>AhDIP</i> and <i>AhLea4</i>. Taken together the results indicate that co-expression of stress responsive TFs can activate multiple CT pathways, and this strategy can be employed to improve abiotic stress tolerance in crop plants.</p></div