Integrated Centre for Drought Research
Department of Crop Physiology, University of Agricultural Sciences, Bengaluru 560 065

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Several diverse and inter-related mechanisms bring in increased level of adaptation to moisture stress. Introgressing a few or several traits into a single genetic background is essential to achieve a comprehensive improvement in drought tolerance coupled with productivity under water limited conditions.  The emphasis has therefore, been to adopt transgenic and/or molecular breeding strategies for trait pyramiding.  This necessitates functional validation of stress transcriptome and identification of QTL that govern constitutive as well as adaptive traits.  These approaches would further lead to the identification of novel genes (superior alleles) and effective genotypes with desirable traits.   A transgenic approach with candidate genes in a desirable genotype with specific traits will improve field level stress adaptation.

COE program support includes 5 inter-related aspects with the ultimate goal of prospecting genes and QTLs and improving the stress adaptation by transgenic and/or MAS. The conceptual framework envisioned is driven by the inputs from these inter-related subprograms.

Project 1: Genes for improving drought traits: Validation of the stress transcriptome of adapted species to identify candidate genes (Drought gene discovery)

The major objective of the sub-program is to analyze stress transcriptome from groundnut and a few outsourced upstream regulatory genes to identify candidate genes and develop and validate over expression cassettes to generate transgenics.

Diverse functional genomic approach (like VIGS, RNAi over expression  studies are being adopted in model systems to validate groundnut stress transcriptome and many other outsourced regulatory genes. Identification of genes regulating cellular level tolerance and those associated with root growth and waxes is the major objective. The validated genes from groundnut cDNA libraries and those outsourced are potential candidate genes to improve stress responses of crop plants. Since several mechanisms are involved in stress adaptation, coordinated expression of validated genes by developing multi-gene expression cassettes is another goal. The approach to develop transformants with stable transgene expression using multi-gene cassettes for candidate gene is quite successful.

Project 2: Cloning stress specific promoters from stress adopted species

The major emphasis is to clone, outsource and validate stress specific promoters which will be used to develop suitable expression vector. Cloning the promoters from highly stress responsive genes of adapted species is the approach. Besides, novel T7 polymerase driven T7 promoter system is being developed to drive the stress genes. In addition a synthetic promoter 4xABRE has been validated as a potential stress inducible promoter. The focus is to develop multi-site expression cassettes with diverse stress inducible promoter.

Project 3: Identification and characterization of genotypes with inherent traits of adaptive significance under drought

The major emphasis to identify superior trait donor parents for inherent traits such as water mining, WUE, water conservation, phenology and other relevant traits

Robust phenotyping approaches using stable isotope signatures (13C and 18O), specialized root structure and other novel laboratory screening tools like Temperature Induction Response Technique (TIR) are employed to phenotype the germplasm accessions/breeding lines. Promising lines with distinct drought tolerance traits have been identified in crops like Rice, sunflower and groundnut.

Project 4: Development and evaluation of transgenics for drought tolerance

The emphasis is to develop robust, reproducible transformation protocols in mandate crops and transgenics expressing relevant stress tolerance genes. Genotypes independent transformation protocols were developed for groundnut, rice and sunflower.

The major objective of this (transgenic approach) is to bring together relevant adaptive traits to one background. Transgenics developed with validated genes in the background of genotypes with superior water relation traits showed significant increase in productivity under water limited conditions compared with the wild-type as well as checks, providing an excellent proof of concept to our conceptual framework. Promising transgenics are being advanced for field evaluation.

Project 5: Trait introgression through molecular breeding to develop rice cultivars suitable for semi-irrigated aerobic condition

Identification of QTLs governing complex drought tolerance traits associated with water mining, WUE and other related traits is the most important emphasis. Identification of superior allele of specific drought tolerance traits through allele mining is yet another major goal.

The approach has been LD based association mapping using a diverse panel of rice accessions.

An excellent panel of rice germplasm lines with significant molecular diversity and as well as phenotypic variability in the traits of interest was identified. The panel is highly suitable for marker trait association through LD mapping. Several tightly associated markers identified.

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