Abstract
Identification and elucidation of functions of plant genes is valuable for both basic and applied research. In addition to natural variation in model plants, numerous loss-of-function resources have been produced by mutagenesis with chemicals, irradiation, or insertions of transposable elements or T-DNA. However, we may be unable to observe loss-of-function phenotypes for genes with functionally redundant homologs and for those essential for growth and development. To offset such disadvantages, gain-of-function transgenic resources have been exploited. Activation-tagged lines have been generated using obligatory overexpression of endogenous genes by random insertion of an enhancer. Recent progress in DNA sequencing technology and bioinformatics has enabled the preparation of genomewide collections of full-length cDNAs (fl-cDNAs) in some model species. Using the fl-cDNA clones, a novel gain-of-function strategy, Fl-cDNA OvereXpressor gene (FOX)-hunting system, has been developed. A mutant phenotype in a FOX line can be directly attributed to the overexpressed fl-cDNA. Investigating a large population of FOX lines could reveal important genes conferring favorable phenotypes for crop breeding. Alternatively, a unique loss-of-function approach Chimeric REpressor gene Silencing Technology (CRES-T) has been developed. In CRES-T, overexpression of a chimeric repressor, composed of the coding sequence of a transcription factor (TF) and short peptide designated as the repression domain, could interfere with the action of endogenous TF in plants. Although plant TFs usually consist of gene families, CRES-T is effective, in principle, even for the TFs with functional redundancy. In this review, we focus on the current status of the gene-overexpression strategies and resources for identifying and elucidating novel functions of cereal genes. We discuss the potential of these research tools for identifying useful genes and phenotypes for application in crop breeding.
Highlights
Modern plant breeding has developed several key technologies in crop breeding that have contributed to increasing and sustaining food production
The results suggested effective silencing of the target genes by the hairpin RNA (hpRNA) library, and a high potential of the rice RNA interference (RNAi) population for genomewide gene identification (Wang L. et al, 2013)
Transgenic rice plants in which the function of IDEF2 was disrupted by RNA interference (RNAi) or Chimeric REpressor gene Silencing Technology (CRES-T) (IDEF2::SRDX under the control of rice Actin-1 constitutive promoter) revealed aberrant iron homeostasis and repression of expression of genes induced under iron deficiency, indicating that IDEF2 functions as a key transcription factor (TF) regulating iron-deficiency response (Ogo et al, 2008)
Summary
Modern plant breeding has developed several key technologies in crop breeding that have contributed to increasing and sustaining food production. Large loss-of-function mutant populations have been generated by activation and random genome insertion of the Tos17 retrotransposon (Hirochika, 2001; Miyao et al, 2003, 2007), Ds and dSpm transposable elements (Upadhyaya et al, 2002; Kolesnik et al, 2004; Kumar et al, 2005; van Enckevort et al, 2005; Park et al, 2007), or T-DNAs (An et al, 2003; Chen et al, 2003; Ryu et al, 2004; Sallaud et al, 2004).
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