editing approaches has played important role in soybean improvement and
gene function studies.
4.9.1 Virus-Induced Gene Silencing: A Potential Biotechnological
Tool for Rapid Elucidation of Genes Function
Although comparative and functional genomic strategies have provided initial clues
about function of abiotic stress-responsive genes in soybean and many other crop
species (Gorantla et al. 2007; Tran and Mochida 2010; Soares-Cavalcanti et al.
2012), comprehensive functional characterization tools are necessary for understanding the precise role of these genes in combating drought stress. One such
tool is virus induced gene silencing (VIGS) which has emerged as a potential gene
knock-down technique in several crop species because it does not require transformation (Baulcombe 1999; Burch-Smith et al. 2004; Senthil-Kumar and Mysore
2011). Virus-induced gene silencing (VIGS) is a reverse genetic tool for functional
elucidation of genes involving gene transcript suppression. In VIGS system, recombinant virus carrying a partial sequence of a host gene is used to infect the plant.
When the virus spreads systemically, the endogenous gene transcripts, which are
homologous to the insert in the VIGS vector, are degraded by post-transcriptional
gene silencing (PTGS) (Baulcombe 1999).
With increased identification of differentially expressed genes employing highthroughput transcript profiling under various abiotic stresses including drought
stress, functional elucidation of stress-responsive genes is crucial to understand
their role in stress tolerance. In recent years, VIGS has been successfully used as a
versatile tool for gene function analysis in various model plants and also in crop
plants like soybean. Viral vector-based silencing of gene of interest and studying the
gene knock-down in plants under stress can be one of the potential options for
assessing functional significance of stress-responsive genes in soybean. Analysis of
stress downregulated as well as stress upregulated genes is crucial for understanding
molecular responses of crop plants to abiotic stresses. A large number of genes
whose expression altered during various abiotic stresses have been identified
through expression profiling, expressed sequence tags (ESTs), and cDNA library
generated from various plant species (Seki et al. 2002; Govind et al. 2009; Marques
et al. 2009; Bohnert et al. 2006; Becker and Lange 2010; Chen et al. 2015;
Ramegowda et al. 2017; Abd El-Daim et al. 2018). However, identifying the
functional significance of individual differentially expressed genes during drought
stress is a challenging task. It is utmost important to elucidate the function of these
stress-responsive genes to understand the mechanism of stress tolerance and also for
characterizing candidate genes contributing tolerance of susceptible species by
genetic engineering. An inventory of genes showing altered expression under several
abiotic stresses has been established for many crop species employing expressed
sequence tag (EST) analysis (Gorantla et al. 2007; Wani et al. 2010; Blair et al.
2011). In contrast to the enormous progress made in generating sequence information, functional analysis of stress-responsive genes is lagging behind.
4 Breeding and Molecular Approaches for Evolving Drought-Tolerant Soybeans
109
gene function studies.
4.9.1 Virus-Induced Gene Silencing: A Potential Biotechnological
Tool for Rapid Elucidation of Genes Function
Although comparative and functional genomic strategies have provided initial clues
about function of abiotic stress-responsive genes in soybean and many other crop
species (Gorantla et al. 2007; Tran and Mochida 2010; Soares-Cavalcanti et al.
2012), comprehensive functional characterization tools are necessary for understanding the precise role of these genes in combating drought stress. One such
tool is virus induced gene silencing (VIGS) which has emerged as a potential gene
knock-down technique in several crop species because it does not require transformation (Baulcombe 1999; Burch-Smith et al. 2004; Senthil-Kumar and Mysore
2011). Virus-induced gene silencing (VIGS) is a reverse genetic tool for functional
elucidation of genes involving gene transcript suppression. In VIGS system, recombinant virus carrying a partial sequence of a host gene is used to infect the plant.
When the virus spreads systemically, the endogenous gene transcripts, which are
homologous to the insert in the VIGS vector, are degraded by post-transcriptional
gene silencing (PTGS) (Baulcombe 1999).
With increased identification of differentially expressed genes employing highthroughput transcript profiling under various abiotic stresses including drought
stress, functional elucidation of stress-responsive genes is crucial to understand
their role in stress tolerance. In recent years, VIGS has been successfully used as a
versatile tool for gene function analysis in various model plants and also in crop
plants like soybean. Viral vector-based silencing of gene of interest and studying the
gene knock-down in plants under stress can be one of the potential options for
assessing functional significance of stress-responsive genes in soybean. Analysis of
stress downregulated as well as stress upregulated genes is crucial for understanding
molecular responses of crop plants to abiotic stresses. A large number of genes
whose expression altered during various abiotic stresses have been identified
through expression profiling, expressed sequence tags (ESTs), and cDNA library
generated from various plant species (Seki et al. 2002; Govind et al. 2009; Marques
et al. 2009; Bohnert et al. 2006; Becker and Lange 2010; Chen et al. 2015;
Ramegowda et al. 2017; Abd El-Daim et al. 2018). However, identifying the
functional significance of individual differentially expressed genes during drought
stress is a challenging task. It is utmost important to elucidate the function of these
stress-responsive genes to understand the mechanism of stress tolerance and also for
characterizing candidate genes contributing tolerance of susceptible species by
genetic engineering. An inventory of genes showing altered expression under several
abiotic stresses has been established for many crop species employing expressed
sequence tag (EST) analysis (Gorantla et al. 2007; Wani et al. 2010; Blair et al.
2011). In contrast to the enormous progress made in generating sequence information, functional analysis of stress-responsive genes is lagging behind.
4 Breeding and Molecular Approaches for Evolving Drought-Tolerant Soybeans
109