2. The trait defines the two major germplasm groups in 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 (?)

4. High resolution mapping (2004)
Vrs1 locus (1916; 1997)
High resolution mapping (2004)

5. Map-based cloning
~ cM interval, 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

8. 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

10. 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

11. Inferring origin
(Re-)Sequence Vrs1
15 2-rows, 16 6-rows
Haplotype analysis defines groups
Phylogenetic analysis: defines 2-row as ancestral

13. 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

14. 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….”

15. 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

16. 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

17. Barley 6,000 years ago + today’s technology
Mascher et al Nature Genetics. 48: