In the growth condition(s) of plants, numerous secondary metabolites (SMs) are produced by them to serve variety of cellular functions essential for physiological processes, and recent increasing evidences have implicated stress and defense response signaling in their production. The type and concentration(s) of secondary molecule(s) produced by a plant are determined by the species, genotype, physiology, developmental stage and environmental factors during growth. This suggests the physiological adaptive responses employed by various plant taxonomic groups in coping with the stress and defensive stimuli. The past recent decades had witnessed renewed interest to study abiotic factors that influence secondary metabolism during in vitro and in vivo growth of plants. Application of molecular biology tools and techniques are facilitating understanding the signaling processes and pathways involved in the SMs production at subcellular, cellular, organ and whole plant systems during in vivo and in vitro growth, with application in metabolic engineering of biosynthetic pathways intermediates.

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Stress and defense responses in plant secondary metabolites production

Resistant Starch〔邦文〕

Plant secondary metabolites (SMs) play important roles in plant survival and in creating ecological connections between other species. In addition to providing a variety of valuable natural products, secondary metabolites help protect plants against pathogenic attacks and environmental stresses. Given their sessile nature, plants must protect themselves from such situations through accumulation of these bioactive compounds. Indeed, secondary metabolites act as herbivore deterrents, barriers against pathogen invasion, and mitigators of oxidative stress. The accumulation of SMs are highly dependent on environmental factors such as light, temperature, soil water, soil fertility, and salinity. For most plants, a change in an individual environmental factor can alter the content of secondary metabolites even if other factors remain constant. In this review, we focus on how individual environmental factors affect the accumulation of secondary metabolites in plants during both biotic and abiotic stress conditions. Furthermore, we discuss the application of abiotic and biotic elicitors in culture systems as well as their stimulating effects on the accumulation of secondary metabolites. Specifically, we discuss the shikimate pathway and the aromatic amino acids produced in this pathway, which are the precursors of a range of secondary metabolites including terpenoids, alkaloids, and sulfur- and nitrogen-containing compounds. We also detail how the biosynthesis of important metabolites is altered by several genes related to secondary metabolite biosynthesis pathways. Genes responsible for secondary metabolite biosynthesis in various plant species during stress conditions are regulated by transcriptional factors such as WRKY, MYB, AP2/ERF, bZIP, bHLH, and NAC, which are also discussed here.

Plant Secondary Metabolite Biosynthesis and Transcriptional Regulation in Response to Biotic and Abiotic Stress Conditions

Regulation of photosynthesis under salt stress and associated tolerance mechanisms.

The necessity to adapt to climate change is even stronger for grapevine than for other crops, because grape berry composition—a key determinant of fruit and wine quality, typicity and market value— highly depends on “terroir” (complete natural environment), on vintage (annual climate variability), and on their interactions. In the same time, there is a strong demand to reduce the use of pesticides. Thus, the equation that breeders and grape growers must solve has three entries that cannot be dissociated: adaptation to climate change, reduction of pesticides, and maintenance of wine typicity. Although vineyard management may cope to some extent to the short–medium-term effects of climate change, genetic improvement is necessary to provide long-term sustainable solutions to these problems. Most vineyards over the world are planted using vines that harbor two grafted plants’ genomes. Although this makes the range of interactions (scion-atmosphere, rootstock-soil, scion-rootstock) more complex, it also opens up wider possibilities for the genetic improvement of either or both the grafted genotypes. Positive aspects related to grapevine breeding are as follows: (a) a wide genetic diversity of rootstocks and scions that has not been thoroughly explored yet; (b) progress in sequencing technologies that allows high-throughput sequencing of entire genomes, faster mapping of targeted traits and easier determination of genetic relationships; (c) progress in new breeding technologies that potentially permit precise modifications on resident genes; (d) automation of phenotyping that allows faster and more complete monitoring of many traits on relatively large plant populations; (e) functional characterization of an increasing number of genes involved in the control of development, berry metabolism, disease resistance, and adaptation to environment. Difficulties involve: (a) the perennial nature and the large size of the plant that makes field testing long and demanding in manpower; (b) the low efficiency of transformation, regeneration and small size of breeding populations; (c) the complexity of the adaptive traits and the need to define more clearly future ideotypes; (d) the lack of shared and integrative platforms allowing a complete appraisal of the genotype-phenotype-environmental links; (e) legal, market and consumer acceptance of new genotypes. The present chapter provides an overview of suitable strategies and challenges linked to the adaptation of viticulture to a changing environment.

Genetic and Genomic Approaches for Adaptation of Grapevine to Climate Change

Food with higher nutritional value is always desired for human health. Rice is the prime staple food in more than thirty developing countries, providing at least 20% of dietary protein, 3% of dietary fat and other essential nutrients. Several factors influence the nutrient content of rice which includes agricultural practices, post-harvest processing, cultivar type as well as manipulations followed by selection through breeding and genetic means. In addition to mutation breeding, genetic engineering approach also contributed significantly for the generation of nutrition added varieties of rice in the last decade or so. In the present review, we summarize the research update on improving the nutritional characteristics of rice by using genetic engineering and mutation breeding approach. We also compare the conventional breeding techniques of rice with modern molecular breeding techniques toward the generation of nutritionally improved rice variety as compared to other cereals in areas of micronutrients and availability of essential nutrients such as folate and iron. In addition to biofortification, our focus will be on the efforts to generate low phytate in seeds, increase in essential fatty acids or addition of vitamins (as in golden rice) all leading to the achievements in rice nutrition science. The superiority of biotechnology over conventional breeding being already established, it is essential to ascertain that there are no serious negative agronomic consequences for consumers with any difference in grain size or color or texture, when a nutritionally improved variety of rice is generated through genetic engineering technology.

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Genetic Manipulation for Improved Nutritional Quality in Rice.

The negative effects of soil salinity towards grape yield depend upon salt concentration, cultivar type, developmental stage, and rootstock. Thompson Seedless variety of grape plant is considered moderately sensitive to salinity when grown upon its own root stock. In recent epoch, identification of key genes responsive to salinity offers hope to generate salinity-tolerant crop plants by their overexpression through genetic manipulation. In the present report, salt responsive transcriptome analysis of Thompson Seedless grape variety was done to identify vital genes involved in salinity tolerance which could be used further to generate salt liberal grape plant or other crop plants. Transcriptome libraries for control and 150-mM-NaCl-treated grape leaves were sequenced on Illumina platform where 714 genes were found to be differentially expressed. Gene ontology analysis indicated that under salinity conditions, the genes involved in metabolic process were highly enriched. Keto Encyclopedia of Genes and Genomes analysis revealed that, among the top 22 enriched pathways for the salt stress upregulated genes, the carbohydrate metabolism, signal transduction, energy metabolism, amino acid metabolism, biosynthesis of secondary metabolite, and lipid metabolism pathways possessed the largest number of transcripts. Key salinity-induced genes were selected and validated through qRT-PCR analysis which was comparable to RNA-seq results. Real-time PCR analysis also revealed that after 24 days of salinity, the expression of most of the selected key genes was highest. These salinity-induced genes will be characterized further in a model plant and also in Vitis vinifera through transgenic approach to disclose their role towards salt tolerance.

Transcriptome analysis of grapevine under salinity and identification of key genes responsible for salt tolerance

Making the first contact with the soil environment, roots are the first responders of soil borne stress including nutrient and water scarcity, hyper salinity and soil compactness. Embryonic root responds by bending, twisting, foraging and regulation of lateral root initiation. Traditional rice cultivars adapted to diverse topography harbour novel stress tolerance traits. We established a quantitative measurement coefficient termed stress adaptation coefficient (SAC) dependent on root responses to stress and applied it to study the effect of mechanical stress and salinity on roots of rice genotypes collected all across West Bengal, India. The responses of root to mechanical and salinity stress are overlapping. Analysis of the response of roots by means of SAC in 28 rice cultivars including high-yield salt tolerant varieties as well as geographically isolated native rice genotypes shows that many of the salt tolerant varieties also perform better in mechanical stress while the opposite is not always true. Transcriptome analysis through cDNA microarray of stress sensitive variety IR64 shows about 6000 common transcripts to be differentially regulated among the two stresses. Quantitative real time expression analyses of salt sensitive and known salt tolerant varieties reveal the involvement of identified genes in salinity and mechanical stress. Overall, our study indicates that there is an important commonality in the molecular basis of salt and mechanical stress and presents an easy-to-perform early establishment stress screen for rice genotypes.

Soil salinity and mechanical obstruction differentially affects embryonic root architecture in different rice genotypes from West Bengal

C3 photosynthesis in rice is dependent on regeneration of Ribulose 1,5-bisphosphate (RuBP), the CO2 acceptor which is largely determined by the Fructose 1,6-bisphosphatase (FBPase) function in the chloroplast. Abiotic stress affects this function negatively impacting the decline in the photosynthetic potential of crop plants. In the present work the PcCFR gene, coding for a salt-tolerant chloroplastic FBPase, from Oryza coarctata (Roxb.) Tateoka, was introduced into the cultivated rice (Oryza sativa var. indica IR64). The homozygous transgenic PcCFR plants performed better than the untransformed lines in terms of overall plant growth, photosynthetic performances and grain yield under normal as well as under salt and different abiotic stress conditions. Under salinity, drought and cold stress PcCFR lines showed tolerance through emergence of new leaves, improved photosynthetic performance and overall growth rate. The cumulative results suggested that the overexpression of salt-tolerant FBPase (PcCFR) protein in the transgenic rice helps to keep the photosynthetic cycle by unabated generation of RuBP that retains better light harvesting capacity of the leaves under stress. It is presumed that this will provide an insight into the growth and development during abiotic stress by inducing an interaction among different sugars derived from photosynthetic carbon metabolism as well. 
The transgenic IR64 plants, over-expressing a salt-tolerant chloroplastic FBPase from Porteresia coarctata, showed multi-stress tolerance, improved plant phenotype, electron transport rate, transpiration rate, photosynthetic efficiency and grain yield under salinity.

A salt‐tolerant chloroplastic FBPase from Oryza coarctata confers improved photosynthesis with higher yield and multi‐stress tolerance to indica rice

Eukaryotic membrane lipids create hydrophobic physical barriers which control information and substance exchange between the outside and inside of cells and also between different cellular compartments. Membrane lipids like Phosphoinositides (PIs) also exert regulatory ef fect on cells in addition to its membrane traf ficking property. Apart from that, phosphoinositide specific phospholipase C (PI-PLC), the enzyme acting upon phosphoinositides, also plays a significant role in exerting such regulatory effect on cell functions. PI-PLCs belong to an important class of enzymes and involved in lipid signalling. The functional mechanism of PI-PLCs is well studied in animal system. Certainly , it is evident that phosphoinositides and phospholipase C both play key roles in plant growth, development and stress tolerance. However, an exact mechanism pertaining to the action of the role of PI-PLC is still under elucidation. In this communication, an attempt has been made to highlight the mechanism of regulation in pla t PI-PLCs and to revisit the area of functioning of PIs and PI-PLCs in response to biotic and in particular abiotic stresses in plants.

http://insa.nic.in/writereaddata/UpLoadedFiles/PINSA/2017_Art57.pdf

Priyanka Das

Papers

Genetic Manipulation for Improved Nutritional Quality in Rice.

Transcriptome analysis of grapevine under salinity and identification of key genes responsible for salt tolerance

Soil salinity and mechanical obstruction differentially affects embryonic root architecture in different rice genotypes from West Bengal

A salt‐tolerant chloroplastic FBPase from Oryza coarctata confers improved photosynthesis with higher yield and multi‐stress tolerance to indica rice

Phosphoinositides and Phospholipase C Signalling in Plant Stress Response: A Revisit