Journal Article

Allelic polymorphism of GIGANTEA is responsible for naturally occurring variation in circadian period in Brassica rapa

D. Loring P. Schaible, C. Robertson McClung, Brent E. Ewers, Hee Jin Park, Cynthia Weinig, Matti Juhani Salmela, Qiguang Xie, Ping Lou, Victor Hermand, Rashid Aman, Woe Yeon Kim, Sarah L. Khan, Dae-Jin Yun

2015

Overview

GIGANTEA ( GI ) was originally identified by a late-flowering mutant in Arabidopsis , but subsequently has been shown to act in circadian period determination, light inhibition of hypocotyl elongation, and responses to multiple abiotic stresses, including tolerance to high salt and cold (freezing) temperature. Genetic mapping and analysis of families of heterogeneous inbred lines showed that natural variation in GI is responsible for a major quantitative trait locus in circadian period in Brassica rapa. We confirmed this conclusion by transgenic rescue of an Arabidopsis gi-201 loss of function mutant. The two B. rapa GI alleles each fully rescued the delayed flowering of Arabidopsis gi-201 but showed differential rescue of perturbations in red light inhibition of hypocotyl elongation and altered cold and salt tolerance. The B. rapa R500 GI allele, which failed to rescue the hypocotyl and abiotic stress phenotypes, disrupted circadian period determination in Arabidopsis . Analysis of chimeric B. rapa GI alleles identified the causal nucleotide polymorphism, which results in an amino acid substitution (S264A) between the two GI proteins. This polymorphism underlies variation in circadian period, cold and salt tolerance, and red light inhibition of hypocotyl elongation. Loss-of-function mutations of B. rapa GI confer delayed flowering, perturbed circadian rhythms in leaf movement, and increased freezing and increased salt tolerance, consistent with effects of similar mutations in Arabidopsis . Collectively, these data suggest that allelic variation of GI —and possibly of clock genes in general—offers an attractive target for molecular breeding for enhanced stress tolerance and potentially for improved crop yield. Significance The plant circadian clock affects many aspects of growth and development and influences both fitness in natural settings and performance in cultivated conditions. We show that GIGANTEA ( GI ) underlies a major quantitative trait locus for circadian period in Brassica rapa by fine-mapping, analysis of heterogeneous inbred lines, and transgenic rescue of an Arabidopsis gi-201 loss-of-function mutant. Analysis of chimeric and mutated B. rapa GI alleles identified the causal nucleotide polymorphism responsible for the allelic variation in circadian period, cold and salt tolerance, and red light inhibition of hypocotyl elongation. Allelic variation of GI and of clock genes in general offers targets for marker-assisted (molecular) breeding for enhanced stress tolerance and potentially for improved crop yield.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Alleles / Amino acids / Arabidopsis / Base Sequence / Biological Sciences / Brassica - genetics / Brassica rapa / breeding / chimerism / Chromosome Mapping / Circadian Rhythm / Circadian rhythms / cold / Crop yield / Exons / Flowers / Flowers & plants / Freezing / Gene Expression Regulation, Plant / Gene mapping / Genetic Complementation Test / genetically modified organisms / Genomics / growth and development / Hypocotyl - metabolism / hypocotyls / inbred lines / Models, Genetic / Molecular Sequence Data / mutants / Mutation / Phenotype / Phenotypes / Plant Proteins - genetics / Plant Proteins - physiology / Polymerase Chain Reaction / Polymorphism / Polymorphism, Single Nucleotide / Proteins / Quantitative Trait Loci / red light / Salt tolerance / Seedlings / stress tolerance / Temperature / Transgenes / Transgenic plants