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Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated protein (Cas) act as an adaptive immune system against invading nucleic acids and bacteriophages in bacteria and archaea. Based on the constitution of effector protein, CRISPR/Cas is broadly divided into multiple types and subtypes. Among these, type VI CRISPR/Cas system is of special attention with four subtypes, namely, VI-A, VI-B, VI-C, and VI-D, and are believed to have evolutionary origin from transposons. These subtypes exhibit variations in structural architecture and mechanism and have diverse Cas13a (C2c2), Cas13b1 (C2c6), Cas13b2 (C2c6), Cas13c (C2c7) and Cas13d effector proteins. CRISPR/Cas13 ribonuclease processes pre-crRNA to mature crRNA which targets and knockdown single-stranded RNA of phage genome during viral interference. The high specificity RNA guiding and RNA-targeting capacity of this protein enables to fuse with several effector molecules, opening new avenues in the field of Cas13-mediated RNA targeting, tracking, and editing. CRISPR/Cas13 has a unique feature of targeting RNAs including plants, so it can be used as a new tool for engineering interference against plant pathogens including RNA viruses, with better specificity and for other RNA modifications in plants. Fluorescent probe-tagged deactivated programmable Cas13 proteins could be used as an alternative tool for in vitro RNA studies. The engineered Cas13 can also be used for programmable RNA editing. The high target specificity, low cost, and user-friendly operation of CRISPR/Cas13 make this an effective tool for several RNA-based research studies and applications. Therefore, the focus of this chapter is upon classification of CRISPR/Cas system, structural and functional diversity of type VI CRISPR/Cas system including its discovery and origin, mechanism, and role of Cas13 in RNA editing of plants.

Sugar alcohols or polyols are derivatives of sugars produced in high amounts during salt or drought (abiotic) stress in plants. A number of sugar alcohols identified in plants include manitol, sorbitol, D-ononitol, pinitol, adonitol, ribitol, glucitol etc., which are classified as cyclic and non-cyclic polyols. Osmoregulation is a phenomenon of regulating constant fluid osmotic pressure in cells through salt and water concentrations during abiotic stress conditions. In plants, abiotic stress induces water loss, and at the same time, they release osmolytes including sugar alcohols which maintains osmoregulation. Sugar alcohols play a crucial role in osmotic adaptations and exert tolerance to salt and drought stress in plants. Due to the importance of sugar alcohols in crop improvement its metaolism, osmotic adaptations and role of transformational studies are discussed in the present chapter.

Groundnut (Arachis hypogaea L.) is one of the important legume cash crops of tropical and semi-arid regions, where it provides a major source of edible oil and vegetable proteins. Abiotic and biotic stresses in groundnut negatively influence on survival, biomass production, and total crop yield. Breeding groundnut genotypes for abiotic stress tolerance will likely sustain groundnut production. Traditional approaches such as breeding for abiotic stress tolerance have been slow, due to the rare alleles implicated in abiotic stress tolerance in the existing groundnut germplasm. Hence, engineering for abiotic stress resistance is an important target for increasing groundnut productivity. The chapter focuses on the development of transgenic groundnut plants for abiotic stress tolerance and the constraints associated with it. This review also describes the recent progress in using genetic engineering approaches for the improvement of abiotic stress tolerance in groundnut.

Plants adapt to a wide range of environments through a sophisticated and efficient signal transduction mechanism by modulating regulatory and functional genes. Crop species exhibit genotypic variation for abiotic stress tolerance and as a result quality and productivity of agriculture crops are drastically affected. To meet the global population demand there is a need for development of stress tolerant crops with improved quality. Since abiotic stress is a multigenic trait the classical breeding approach fails to develop stress tolerance traits, thus the transgenic approach is being successfully applied to produce stress tolerant crops. Unraveling the abiotic stress signal sensing and transduction molecules augments our capability to improve stress tolerant crops to attain sustainable agriculture development. In this chapter, we mainly focused on abiotic stress-induced signaling molecules and discussed recent progress of engineering signaling molecules of the abiotic stress signaling pathway and their possible role in abiotic stress tolerance.

Peanut is an important oilseed and food legume cultivated as a rain-fed crop in semi-arid tropics. Drought and high salinity are the major abiotic stresses limiting the peanut productivity in this region. Development of drought and salt tolerant peanut varieties with improved yield potential using biotechnological approach is highly desirable to improve the peanut productivity in marginal geographies. As abiotic stress tolerance and yield represent complex traits, engineering of regulatory genes to produce abiotic stress-resilient transgenic crops appears to be a viable approach. In the present study, we developed transgenic peanut plants expressing an Arabidopsis homeodomain-leucine zipper transcription factor (AtHDG11) under stress inducible rd29A promoter. A stress-inducible expression of AtHDG11 in three independent homozygous transgenic peanut lines resulted in improved drought and salt tolerance through up-regulation of known stress responsive genes (LEA, HSP70, Cu/Zn SOD, APX, P5CS, NCED1, RRS5, ERF1, NAC4, MIPS, Aquaporin, TIP, ELIP) in the stress gene network, antioxidative enzymes, free proline along with improved water use efficiency traits such as longer root system, reduced stomatal density, higher chlorophyll content, increased specific leaf area, improved photosynthetic rates, and increased intrinsic instantaneous WUE. Transgenic peanut plants displayed high yield compared to non-transgenic plants under both drought and salt stress conditions. Holistically, our study demonstrates the potentiality of stress-induced expression of AtHDG11 to improve the drought, salt tolerance in peanut.