BGS 67, Six-rowed spike 1 (deficiens spike), Vrs1.t

Historically, alleles at the six-rowed spike 1 (vrs1) locus were included in several Barley Genetic Stock (BGS) descriptions even though they were known to be alleles at the same locus. The most common spike type variant is the six-rowed allele (vrs1.a) (3, 6, 7). Other alleles at the vrs1 locus are described in BGS 6, BGS 58, and BGS 66.

Hordeum deficiens = V (5).
Hordeum deficiens = Vt (11).
Renamed Vrs1.t based on allelism tests. (7).
Mutation in homeodomain-leucine zipper I-class homeobox = HvHox1 (3, 6).

Monofactorial incomplete dominant (6); the Vrs1.t1 allele is the most dominant allele in the multiple allelic series at the vrs1 (six-rowed spike 1) locus (11), but interacts as an incomplete dominant with some alleles (2, 7)..
Located in chromosome 2HL (8, 10); the vrs1.t locus is about 15.4 cM distal from the Toothed lemma 1 (Gth1) locus (10); vrs1.t is about 30.5 cM distal from the eog1 (elongated outer glume 1) locus (8). Vrs1.t1 is associated with SNP markers 2_0781 to 2_1351 (positions 135.19 to 145.80 cM) in 2H bins 09 to 10 of the Bowman backcross-derived line BW900 (1).

Plants homozygous for Vrs1.t1 (Vt) allele always have a deficiens phenotype regardless of the allele present at the int-c (intermedium spike-c) locus in chromosome 4H. Deficiens is characterized by the extreme reduction in size of lateral spikelet (11). The Vrs1.t1 allele in Engleawnless does not recombine with the Lks1.a allele at the Lks1 (Awnless) locus because a short paracentric inversion is present in this stock (9). Plants in Bowman backcross-derived line for Vrs1.t1 (BW900) were similar to Bowman except spikes had 1 to 2 more kernels per spike, and kernels were about 10% lighter (2). Expression of the Vrs1 gene is strictly localized in the lateral-spikelet primordia of immature spikes suggesting that the VRS1 protein suppresses development of lateral spikelets (3). Re-sequencing a 2.1 kb fragment region including the HvHox1 region of the vrs1 locus found that the six-rowed variants (vrs1.a1, vrs1.a2 and vrs1.a3) and the deficiens variant (Vrs1.t1) had isoforms different from those of wild barleys and two-rowed barleys (6). Plants with Vrs1.t1 gene had smaller lateral spikelet meristems compared with the typical two-rowed type (7). Transcriptome analysis revealed that a number of histone superfamily genes were upregulated in the deficiens mutant suggesting that enhanced cell proliferation in the central spikelet may contribute to larger kernel size (7).

Natural occurrence in two-rowed barleys from Ethiopia previously classified as Hordeum deficiens (12). Haplotype analysis revealed that barley carrying the deficiens allele (Vrs1.t1) originated from two-rowed types carrying the Vrs1.b2 allele, which is predominantly found in germplasm from Northern Africa (7).

Vrs1.t or Vt in White Deficiens (CIho 7316, GSHO 684) (7, 12); Vrs1.t2 (Deficiens 2) (NGB 115174), Vrs1.t3 (Semi-deficiens 12) (NGB 115188) in Foma (NGB 14659, CIho 11333) (4, 7).

Vrs1.t1 (Vt) in White Deficiens (GSHO 684); Vrs1.t1 in Bowman (PI 483237)*8 (GSHO 1909, BW900, NGB 22332).

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2. Franckowiak, J.D. (Unpublished).
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4. Lundqvist, U. (Unpublished).
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