Download Slides - Barley World

Barley
2n = 2x = 14
~ 5,300 Mb
Two-row vs. six-row
The trait defines the two major
germplasm groups in barley
A reproductive fitness trait:
6-row 3X more yield than 2-row (?)
Vrs1 locus (1916; 1997)
High resolution mapping (2004)
Map-based cloning
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~ 0.07 cM interval, 9.831 gametes
6 Bacterial Artificial Chromosomes (518 Kb)
Three genes, 1 degenerate
HvHox1 lies between flanking markers
Wild type (2-row) ORF = 222 aa polypeptide
• HD-ZIP motif
Expression
HD-ZIP I (HvHox1) stage- and tissue-specific in 2-row
• Transcription levels of Vrs1
• Abundant early in spike development, then taper off
• In situ hybridization localizes expression to lateral
spikelet primordia, no expression in central spikelet
primordia
Mutant survey
• 57 mutants (6-row) derived from 2-row and allelic at
Vrs1
• Lesions in Vrs1 correlated with 6-row phenotype in
48/57mutants
• 21 aa substitutions
• 12 truncated protein due to premature stop codon
• 3 SNPs at intron splice sites
• 5 frameshifts
• 7 complete deletion of the gene: Vrs1 is dispensable
• 9 mutants no DNA change in coding region:
• 7/9 no expression: regulatory mutations
• 2 expression = 2-row: post-translational modification
Inferring origin
(Re-)Sequence Vrs1
• 15 2-rows, 16 6-rows
• Haplotype analysis defines groups
• Phylogenetic analysis: defines 2-row as ancestral
Discussion
2-row ancestral; 6-row = loss of function = recessive
• Vrs1 encodes HD-ZIP transcription factor
• Sequence
• Expression
• No transformation
• HD-ZIPs and plant developmental processes
• Vrs1 encodes a repressor protein that binds to a gene (or
genes) that regulate lateral spikelet fertility
Discussion
(At least) 3 independent processes gave rise to 6-row (but
not necessarily origins) BUT there were likely multiple
origins..
• Haplotypes could not be
• achieved by intragenic recombination after
hybridization
• Explained by simple mutation
• “Six-rowed barley originated independently at different
times and in different regions….probably as a result of
conscious selection by delighted farmers….”
Discussion
Domestication and dispersal
• ~8000 years ago 2-row and 6-row
• Then 6-row dominates
• 2-row re-appears in Fertile Crescent 1,000 years ago
• 2-row arrives in Europe 900 years ago
• Detailed analysis of archaeological specimens required
Discussion
Long-term evolution
• Continuous reduction – from panicle (e.g. rice) to 3
spikelets in barley to 1 spikelet from wheat to
Next step
Poaceae-wide assessment of variability of Vrs1 orthologs
Domestication and dispersal
Barley 6,000 years ago + today’s technology
Mascher et al. 2016. Nature Genetics. 48: 1089-1093.