Glutathione S-transferases (GSTs) are multifunctional proteins encoded by large gene family in plants, which play important role in cellular detoxification of several endobiotic and xenobiotic compounds. Previously, we suggested the diverse roles of rice GST gene family members in plant development and various stress responses based on their differential expression. In this study, we report the functional characterization of a rice tau class GST gene, OsGSTU4. OsGSTU4 fusion protein was found to be localized in nucleus and cytoplasm. The over-expression of OsGSTU4 in E. coli resulted in better growth and higher GST activity under various stress conditions. Further, we raised over-expression transgenic Arabidopsis plants to reveal its in planta function. These transgenic lines showed reduced sensitivity towards plant hormones, auxin and abscisic acid. Various analyses revealed improved tolerance in transgenic Arabidopsis plants towards salinity and oxidative stresses, which may be attributed to the lower accumulation of reactive oxygen species and enhanced GST activity. In addition, microarray analysis revealed up-regulation of several genes involved in stress responses and cellular detoxification processes in the transgenic plants as compared to wild-type. These results suggest that OsGSTU4 can be used as a good candidate for the generation of stress-tolerant crop plants.

 Pm1a, the first powdery mildew resistance gene described in wheat, is part of a complex resistance (R) gene cluster located in a distal region of chromosome 7AL that has suppressed genetic recombination.  A nucleotide-binding, leucine-rich repeat (NLR) immune receptor gene was isolated using mutagenesis and R gene enrichment sequencing (MutRenSeq). Stable transformation confirmed Pm1a identity which induced a strong resistance phenotype in transgenic plants upon challenge with avirulent Blumeria graminis (wheat powdery mildew) pathogens.  A high-density genetic map of a B. graminis family segregating for Pm1a avirulence combined with pathogen genome resequencing and RNAseq identified AvrPm1a effector gene candidates. In planta expression identified an effector, with an N terminal Y/FxC motif, that induced a strong hypersensitive response when co-expressed with Pm1a in Nicotiana benthamiana.  Single chromosome enrichment sequencing (ChromSeq) and assembly of chromosome 7A suggested that suppressed recombination around the Pm1a region was due to a rearrangement involving chromosomes 7A, 7B and 7D. The cloning of Pm1a and its identification in a highly rearranged region of chromosome 7A provides insight into the role of chromosomal rearrangements in the evolution of this complex resistance cluster.

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The medicinal plant, Catharanthus roseus, accumulates wide range of terpenoid indole alkaloids, which are well documented therapeutic agents. In this study, deep transcriptome sequencing of C. roseus was carried out to identify the pathways and enzymes (genes) involved in biosynthesis of these compounds. About 343 million reads were generated from different tissues (leaf, flower and root) of C. roseus using Illumina platform. Optimization of de novo assembly involving a two-step process resulted in a total of 59,220 unique transcripts with an average length of 1284 bp. Comprehensive functional annotation and gene ontology (GO) analysis revealed the representation of many genes involved in different biological processes and molecular functions. In total, 65% of C. roseus transcripts showed homology with sequences available in various public repositories, while remaining 35% unigenes may be considered as C. roseus specific. In silico analysis revealed presence of 11,620 genic simple sequence repeats (excluding mono-nucleotide repeats) and 1820 transcription factor encoding genes in C. roseus transcriptome. Expression analysis showed roots and leaves to be actively participating in bisindole alkaloid production with clear indication that enzymes involved in pathway of vindoline and vinblastine biosynthesis are restricted to aerial tissues. Such large-scale transcriptome study provides a rich source for understanding plant-specialized metabolism, and is expected to promote research towards production of plant-derived pharmaceuticals.

Auxin is among the key growth regulators that play diverse roles in virtually all aspects of plant growth and development. Intensive investigations during the past two decades have helped in elucidation of auxin perception and signal transduction mechanisms operative in plants. In addition to its primary role in regulating plant development, several studies in recent years have provided unfl inching evidence for the involvement of auxin in abiotic stress responses. Functional genomics studies and genome-wide expression analysis have revealed altered expression of auxin-responsive genes, such as Aux/IAA , GH3 , SAURs , and ARFs , under abiotic stress conditions . Variations in endogenous levels of auxin at global and local levels under various abiotic stress conditions have been associated with phenotypic changes and provided intriguing evidences regarding its role in response to environmental changes. Modulation of reactive oxygen species (ROS) levels in response to exogenous auxin as well as to drought, salinity, and ABA have indicated towards a complex relationship network between auxin, ROS, and abiotic stresses in plants. The advent of recent functional genomics technologies has led to identifi cation of several candidate genes that may modulate crosstalk between auxin and abiotic stresses. This chapter discusses auxin homeostasis, signal transduction mechanisms, and how these processes are modulated under abiotic stresses, thus emphasizing on the emerging roles of auxin as a key integrator of abiotic stress pathways and plant development.