Six-rowed barley originated from a mutation in a homeodomain-leucine zipper I-class homeobox gene.
Increased seed production has been a common goal during the domestication of cereal crops, and early cultivators of barley (Hordeum vulgare ssp. vulgare) selected a phenotype with a six-rowed spike that stably produced three times the usual grain number. This improved yield established barley as a founder crop for the Near Eastern Neolithic civilization. The barley spike has one central and two lateral spikelets at each rachis node. The wild-type progenitor (H. vulgare ssp. spontaneum) has a two-rowed phenotype, with additional, strictly rudimentary, lateral rows; this natural adaptation is advantageous for seed dispersal after shattering. Until recently, the origin of the six-rowed phenotype remained unknown. In the present study, we isolated vrs1 (six-rowed spike 1), the gene responsible for the six-rowed spike in barley, by means of positional cloning. The wild-type Vrs1 allele (for two-rowed barley) encodes a transcription factor that includes a homeodomain with a closely linked leucine zipper motif. Expression of Vrs1 was strictly localized in the lateral-spikelet primordia of immature spikes, suggesting that the VRS1 protein suppresses development of the lateral rows. Loss of function of Vrs1 resulted in complete conversion of the rudimentary lateral spikelets in two-rowed barley into fully developed fertile spikelets in the six-rowed phenotype. Phylogenetic analysis demonstrated that the six-rowed phenotype originated repeatedly, at different times and in different regions, through independent mutations of Vrs1.
Komatsuda
Takao
T
National Institute of Agrobiological Sciences, Tsukuba 305-8602, Japan. takao@affrc.go.jp
Pourkheirandish
Mohammad
M
He
Congfen
C
Azhaguvel
Perumal
P
Kanamori
Hiroyuki
H
Perovic
Dragan
D
Stein
Nils
N
Graner
Andreas
A
Wicker
Thomas
T
Tagiri
Akemi
A
Lundqvist
Udda
U
Fujimura
Tatsuhito
T
Matsuoka
Makoto
M
Matsumoto
Takashi
T
Yano
Masahiro
M
D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D017931:DNA Primers; D005801:Genes, Homeobox; D017343:Genes, Plant; D001467:Hordeum / Q000235:genetics*; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D009154:Mutation
D017931:DNA Primers