ABSTRACT
Genetic differentiation in 20 hierarchically sampled populations of wild barley was analyzed with quantitative traits, allozymes and Random Amplified Polymorphic DNAs (RAPDs), and compared for three marker types at two hierarchical levels. Regional subdivision for both molecular markers was much lower than for quantitative traits. For both allozymes and RAPDs, most loci exhibited minor or no regional differentiation, and the relatively high overall estimates of the latter were due to several loci with exceptionally high regional differentiation. The allozyme- and RAPD-specific patterns of differentiation were concordant in general with one another, but not with quantitative trait differentiation. Divergent selection on quantitative traits inferred from very high regional Q(ST) was in full agreement with our previous results obtained from a test of local adaptation and multilevel selection analysis. In contrast, most variation in allozyme and RAPD variation was neutral, although several allozyme loci and RAPD markers were exceptional in their levels of regional differentiation. However, it is not possible to answer the question whether these exceptional loci are directly involved in the response to selection pressure or merely linked to the selected loci. The fact that Q(ST) and F(ST) did not differ at the population scale, that is, within regions, but differed at the regional scale, for which local adaptation has been previously shown, implies that comparison of the level of subdivision in quantitative traits, as compared with molecular markers, is indicative of adaptive population differentiation only when sampling is carried out at the appropriate scale.
Subject(s)
Adaptation, Biological/genetics , Genetic Variation , Genetics, Population , Hordeum/genetics , Genetic Markers , Isoenzymes/genetics , Quantitative Trait Loci , Quantitative Trait, Heritable , Random Amplified Polymorphic DNA Technique , Selection, GeneticABSTRACT
Water deficit and the resulting osmotic stress affect plant growth. To understand how plant cells monitor and respond to osmotic change from water stress, we isolated a cDNA from dehydrated Arabidopsis plants. This cDNA encodes a novel hybrid-type histidine kinase, ATHK1. Restriction fragment length polymorphism mapping showed that the ATHK1 gene is on chromosome 2. The predicted ATHK1 protein has two putative transmembrane regions in the N-terminal half and has structural similarity to the yeast osmosensor synthetic lethal of N-end rule 1 (SLN1). The ATHK1 transcript was more abundant in roots than other tissues under normal growth conditions and accumulated under conditions of high or low osmolarity. Histochemical analysis of beta-glucuronidase activities driven by the ATHK1 promoter further indicates that the ATHK1 gene is transcriptionally upregulated in response to changes in external osmolarity. Overexpression of the ATHK1 cDNA suppressed the lethality of the temperature-sensitive osmosensing-defective yeast mutant sln1-ts. By contrast, ATHK1 cDNAs in which conserved His or Asp residues had been substituted failed to complement the sln1-ts mutant, indicating that ATHK1 functions as a histidine kinase. Introduction of the ATHK1 cDNA into the yeast double mutant sln1Delta sho1Delta, which lacks two osmosensors, suppressed lethality in high-salinity media and activated the high-osmolarity glycerol response 1 (HOG1) mitogen-activated protein kinase (MAPK). These results imply that ATHK1 functions as an osmosensor and transmits the stress signal to a downstream MAPK cascade.
Subject(s)
Arabidopsis/enzymology , Protein Kinases/metabolism , Amino Acid Sequence , Arabidopsis/genetics , Base Sequence , Cell Membrane/enzymology , Chromosome Mapping , DNA Primers/genetics , DNA, Complementary/genetics , DNA, Plant/genetics , Genes, Plant , Genetic Complementation Test , Histidine Kinase , Molecular Sequence Data , Mutation , Osmotic Pressure , Plant Roots/enzymology , Protein Kinases/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA, Plant/genetics , RNA, Plant/metabolism , Saccharomyces cerevisiae/genetics , Sequence Homology, Amino Acid , TemperatureABSTRACT
Four cDNAs that encode two-component response regulator-like proteins were cloned from Arabidopsis thaliana. Putative proteins (ATRR1-4) contain a receiver domain with a conserved aspartate residue - a possible phosphorylation site - at the N-terminal half. ATRR2 lacks the C-terminal half; the others contain a C-terminal domain abundant in acidic amino acids or proline residues. ATRR1 and ATRR2 are expressed more in roots than in other tissues and are induced by low temperature, dehydration and high salinity. Levels of ATRR3 and ATRR4 were not affected by stress treatments. These results suggest that ATRRs play distinct physiological roles in Arabidopsis, and that some are involved in stress responses.
