BGS 184, Zeocriton 3, Zeo3

Since the zeocriton spike phenotype was studied by Hayes and Harlan (8), the recommended locus name is Zeocriton 1 (Zeo1). The semi-dominant dense spike variants at the complex Zeo1 locus exhibit a range of phenotypes associated with restricted elongation of the rachis internodes. Based on DNA sequencing, three distinct phenotypic groups of dense spike variants are associated with the Hordeum vulgare APELATA2 (AP2)-like transcription factor (HvAP2) locus (10, 11). The phenotypic expressions were historical assigned different locus symbols, but each group is now associated with specific molecular changes in the HvAP2 transcript (10). Alleles at this locus are assigned locus symbols: the Zeo1 (BGS 082) mutants exhibit the most extreme phenotypes; the Zeo2 variants have intermediate phenotypes; and the Zeo3 variants may show a lesser degree in shortening of rachis internodes (10). Molecular markers and/or pedigree information are necessary to separate variants assigned to the Zeo2 (BGS 614) and Zeo3 (BGS 184) groups (10).

Zeocriton with no gene symbol (4, 8).
Semidwarf mutant in Morex = Mo1 (15).
Zeocriton h = Zeo.h (6).
Cleistogamy 1 = cly1.c (10, 11, 14).
Hordeum vulgare APELATA2 (AP2)-like transcription factor = HvAP2 (10, 11).

Monofactorial dominant (9, 13).
Located in chromosome 2HL (2, 13); Zeo3.d is associated with SNP markers 1_1118 to 2_0494 (positions 180.85 to 221.70 cM) in 2HL bins 11 to 14 of Bowman backcross-derived line BW933; Zeo3.h is associated with SNP markers 2_1125 to 2_0943 (positions 206.17 to 237.13 cM) in 2HL bins 13 to 14 of the Bowman backcross-derived line BW940; Zeo3.j is associated with SNP markers 2_1370 to 1_1023 (positions 199.54 to 224.35 cM) in 2HL bins 12 to 14 of the Bowman backcross-derived line BW936; Zeo3.av (formerly named dsp.av) is associated with SNP markers 1_1236 to 2_0561 (positions 184.46 to 247.96 cM) in 2HL bins 11 to 15 of the Bowman backcross-derived line BW369 (2); the HvAP2 locus is near marker BOPA2_12_10579 and these Bowman lines have the same single base pair change in the microRNA172 binding site (9), in 2H bin 13. Bowman backcross-derived lines BW660 (Zeo3.g) and BW661(Zeo3.i) have the same change at the microRNA172 binding site (9) and SNP markers associated with dense spike mutants ert-c.1 and ert-d.7 in chromosomes 3HL and 7HS, respectively (2).

Hayes and Harlan (8) reported that three genes controlled rachis internode length in their cross to Zeocriton. One of these genes produced strap-shaped spikes with shortened rachis (8). Identification of Bowman backcross-derived lines with the Zeo3 gene was based on DNA sequencing of the HvAP2 gene (10). A similar degree of rachis internode shortening was observed in Bowman backcross-derived lines with either the Zeo2 or the Zeo3 sequence changes in the HvAP2 gene (6, 10). Mutants at Zeo3 are apparently in some cultivars identified as having small lodicules (closed flowering or cleistogamy) (9, 13). The original Zeo3.h (Mo1) mutant differed from the parental cultivar Morex (CIho 15773) in plant height, tiller number, grain yield, and grain quality (12). The Bowman backcrossed lines for Zeo2 and Zeo3 have similar rachis internode lengths, but variability among cultivars with the same genes was observed (10). The rachis internode length of plants in Bowman backcross-derived lines for Zeo3 alleles averaged 3.3 mm compared to 4.5 mm for Bowman. In some test environments, the BW lines with the Zeo3 genes had 1 to 2 more kernels per spike than Bowman, and kernel weights were slightly lower. No effects of the Zeo3 gene on plant height and grain yield were observed (5). DNA sequencing showed that the Zeo1 mutants occur in a Hordeum vulgare APELATA2 (AP2)-like transcription factor, HvAP2. The dense spike and cleistogamous (small lodicules) phenotypes are a consequence of a perturbed interaction between microRNA 172 (Hv-miR172) and its corresponding binding site on the mRNA from the HvAP2 gene, which acts early in spike development to regulate turnover of HvAP2 mRNA (10, 11).

A naturally and induced mutants occurring variant in the fourth exon of the HvAP2 locus (10, 11). A sodium azide induced mutant in Morex (CIho 15773) (15).

Based on haplotypes similarity for in the HvAP2 gene, the potential Zeo3 alleles can be placed in one group (10, 11). The Zeo3 mutant is present in Tammi (OUU059, PI 175505) and a few other cultivars (11) and in Harry (NGB 2666, PI 491575) and in several other cultivars (10). Zeo3.d was isolated from line with a male sterile mutant in P11 (CIho 15836) from Finland (1). The Bowman backcross-derived stocks with Zeo3.g, Zeo3.i, and Zeo3.av were isolated from Finnish cultivars Aapo (PI 467771) and Pokko (PI 467770) (2). Zeo3.h (WA11094-81, GSHO 1611) identified as Mo1 from Morex (CIho 15773) (7, 15), and Zeo3.j (SA121-4-5, GSHO 1612) from Glenn (CIho 15769) (4) were isolated as spike density variants from North American six-rowed cultivars. The SNP markers retained in Bowman backcross-derived lines, BW936 with Zeo3.h and BW940 with Zeo3.j, suggest that these two variants originated independent of the Bowman backcrose-derived lines having Finish cultivars as donor parents (2, 5).

Zeo3.d from P11 (CIho 15836) in Bowman*7 (BW933, NGB 22362); Zeo3.av from Aapo (PI 467771) via Pokko (PI 467770) in Bowman*4 (BW269, NGB 22094); Zeo3.g and Zeo3.i, both with another dense spike gene, from Aapo (PI 467771) via Pokko (PI 467770) in Bowman*7 (BW660, NGB 22225; and BW661, NGB 22226), respectively; Zeo3.h (Mo1, Wa11094-81, GSHO 1611) (formerly listed as Zeo2.h) in Morex (CIho 15773); Zeo3.h in Bowman*5 (GSHO 1999); Zeo3.h from Morex in Bowman*8 (BW940, NGB 22369); Zeo3.j (SA121-4-5, GSHO 1612) from Glenn (CIho 15769) in Bowman*7 (GSHO 1882, BW936, NGB 22365).

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