title: Enhanced Gene Expression Rather than Natural Polymorphism in Coding Sequence of the OsbZIP23 Determines Drought Tolerance and Yield Improvement in Rice Genotypes.
abstract: Drought is one of the major limiting factors for productivity of crops including rice (Oryza sativa L.). Understanding the role of allelic variations of key regulatory genes involved in stress-tolerance is essential for developing an effective strategy to combat drought. The bZIP transcription factors play a crucial role in abiotic-stress adaptation in plants via abscisic acid (ABA) signaling pathway. The present study aimed to search for allelic polymorphism in the OsbZIP23 gene across selected drought-tolerant and drought-sensitive rice genotypes, and to characterize the new allele through overexpression (OE) and gene-silencing (RNAi). Analyses of the coding DNA sequence (CDS) of the cloned OsbZIP23 gene revealed single nucleotide polymorphism at four places and a 15-nucleotide deletion at one place. The single-copy OsbZIP23 gene is expressed at relatively higher level in leaf tissues of drought-tolerant genotypes, and its abundance is more in reproductive stage. Cloning and sequence analyses of the OsbZIP23-promoter from drought-tolerant O. rufipogon and drought-sensitive IR20 cultivar showed variation in the number of stress-responsive cis-elements and a 35-nucleotide deletion at 5'-UTR in IR20. Analysis of the GFP reporter gene function revealed that the promoter activity of O. rufipogon is comparatively higher than that of IR20. The overexpression of any of the two polymorphic forms (1083 bp and 1068 bp CDS) of OsbZIP23 improved drought tolerance and yield-related traits significantly by retaining higher content of cellular water, soluble sugar and proline; and exhibited decrease in membrane lipid peroxidation in comparison to RNAi lines and non-transgenic plants. The OE lines showed higher expression of target genes-OsRab16B, OsRab21 and OsLEA3-1 and increased ABA sensitivity; indicating that OsbZIP23 is a positive transcriptional-regulator of the ABA-signaling pathway. Taken together, the present study concludes that the enhanced gene expression rather than natural polymorphism in coding sequence of OsbZIP23 is accountable for improved drought tolerance and yield performance in rice genotypes.
authors.affiliation: Adv. Lab. for Plant Genetic Engineering, Advanced Technology Development Center, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
authors.forename: Avishek
authors.initials: A
authors.lastname: Dey
authors.affiliation: Adv. Lab. for Plant Genetic Engineering, Advanced Technology Development Center, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
authors.forename: Milan Kumar
authors.initials: MK
authors.lastname: Samanta
authors.affiliation: Adv. Lab. for Plant Genetic Engineering, Advanced Technology Development Center, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
authors.forename: Srimonta
authors.initials: S
authors.lastname: Gayen
authors.affiliation: Adv. Lab. for Plant Genetic Engineering, Advanced Technology Development Center, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
authors.forename: Soumitra K
authors.initials: SK
authors.lastname: Sen
authors.affiliation: Adv. Lab. for Plant Genetic Engineering, Advanced Technology Development Center, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.|Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
authors.forename: Mrinal K
authors.initials: MK
authors.lastname: Maiti
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000222:Adaptation, Physiological / Q000235:genetics*; D000483:Alleles; D001483:Base Sequence; D003001:Cloning, Molecular; D055864:Droughts; D018628:Gene Dosage; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D017343:Genes, Plant; D017930:Genes, Reporter; D005838:Genotype; D018525:Germination / Q000187:drug effects; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics*; D012275:Oryza / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D018384:Oxidative Stress / Q000187:drug effects / Q000235:genetics; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics; D014867:Water
chemical_list: D010940:Plant Proteins; D012333:RNA, Messenger; D014867:Water; D049452:Green Fluorescent Proteins; D000040:Abscisic Acid