Barley dwarfs acting big in agronomy. Identification of genes and characterization of proteins involved in dwarfism, lodging resistance and crop yield
Zusammenfassung der Projektergebnisse
The present report summarizes my activities as a DFG financed postdoctoral researcher at the Carlsberg Laboratory, Copenhagen, and describes future perspectives including the plan to apply for the Emmy Noether fellowship of DFG in order to continue my research activities in Germany. Changing climate conditions and the ever-growing world population call for accelerated and sustainable crop breeding. Since the 1930‘s, thousands of morphological barley mutants have been induced and isolated in breeding programs all over the world to improve crop architecture. Many mutations were utilized to produce high-yielding cultivars, although the genetic origin causing the mutant phenotype was not known. The identification and characterization of mutated genes in historic barley lines provide insight into specific gene functions and can thus support predictive breeding and improvement of crop productivity in modern cultivars. In this context, historical barley semi-dwarf mutants of the groups semi-brachytic (uzu), brachytic (brh), breviaristatum (ari), erectoides (ert) and dense spike (dsp) were studied to characterize individual genes involved in crop development and architecture. A first mapping experiment focused on the identification of the barley loci ert-a and ert-m via SNP marker assisted mapped base cloning. Mutant ert-m was fine-mapped in the center of the short arm of chromosme 7H and successfully cloned as ERECTA-LIKE (ERL) receptor-like kinase in collaboration with Katharina Ahmann. The phenotypical analysis of 20 independent ert-m mutations identified HvERL as a regulator of culm and rachis internode development. Remarkable was the discovery of a fascinating “cross-row” spike phenotype caused by opposite spikelets and twisted rachis internodes. Understanding how to control this specific phenotype in barley will open interesting options for new spike architectures in modern cultivars. The second locus, ert-a, a short straw mutant with striking lodging resistance and dense spike, could be relocated into the centromere of 7H. Further fine-mapping of the locus was proved to be challenging due to the low number of recombination events in the centromeric region. At the same time, the locus dense spike-ar (dsp.ar) was fine-mapped into the same region by Stein and coworkers at IPK Gatersleben. Crossings of ert-a with dsp.ar proved both mutants to be allelic. In collaboration with the group of Stein, a state-of-the-art whole exome capture experiment was started to identify the mutant locus ert-a/dsp.ar. A second gene hunting experiment focused on in silico gene mapping. The phenotype caused by the mutation of the known brassinosteroid (BR) receptor gene HvBRI1 was studied in the East Asian semi-dwarf cultivar uzu in detail and was shown to be temperature-sensitive. HvBRI1 was in silico mapped in the centromere of chromosome 3H and two new alleles of HvBRI1, ari.256 and ert-ii, were identified by a SNP-based sequencing screen of Bowman near isogenic barley lines. Modeling of the individual mutations into the protein structure highlighted the function of the BR binding domain. In contrast to the widespread uzu mutation, the two new alleles showed no temperature-sensitive phenotype supporting the idea of predictive breeding. The specific combination of phenotypes seen in HvBRI1 mutants was found in many barley semi-dwarfs. BR biosynthesis genes were mapped in silico in collaboration with Damian Gruszka and candidate mutants were chosen based on mutant donor introgressions. At present, the five semi-dwarf loci (ari-o, brh.af, brh14, ert-u and ert-zd) could be identified as HvDIM/DWF1 (Diminuto Dwarf) mutants, three loci (ari.245, brh3 and ert-t) as HvBRD1 (Brassinosteroid-6-Oxidase1) mutants and two loci (brh13 and brh18) as HvCPD (Constitutive Photomorphogenic Dwarf) mutants. The screen is still in progress and additional experiments including allelism tests, cosegregation studies and BR complementation tests should verify the candidate genes. The identified mutants have an uzu-like phenotype featuring upright growth for dense planting and a strong culm with increased lodging resistance. The described experiment defines a short cut in barley gene hunting and can be implemented using either a synteny approach or the recently published barley physical genome map. Cloning and expression of identified genes is currently in progress in order to study protein structure and function in detail. Especially, plant specific receptors like HvBRI1, HvERL as well as many of the remaining 600 receptor-like kinases are exciting objects for future research projects as they can be considered key regulators of plant architecture and development, and thus target genes for the production of economically useful barley cultivars.
Projektbezogene Publikationen (Auswahl)
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(2012) Characterization of mutations in barley fch2 encoding chlorophyllide a oxygenase. Plant Cell. Physiol., 53, 1232-1246
Müller, A. H., Dockter, C., Gough, S. P., Lundqvist, U., von Wettstein, D., and Hansson, M.
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(2012) Induced mutations in circadian clock regulator Mat-a facilitated short-season adaptation and range extension in cultivated barley. Proc. Natl. Acad. Sci. USA, 109, 4326-31
Zakhrabekova, S., Gough, S. P., Braumann, I., Müller, A. H., Lundqvist, J., Ahmann, K., Dockter C., Matyszczak, I., Kurowska, M., Druka, A., Waugh, R., Graner, A., Stein N., Steuernagel, B., Lundqvist, U., and Hansson, M.
