BGS 82, Zeocriton 1, Zeo1

Since the zeocriton spike phenotype was first described by Hayes and Harlan (8), Zeo1 became the recommended locus symbol for various mutants at this locus. 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, 13). The phenotypic expressions were historical assigned different locus symbols, but each group is associated with specific molecular changes in the HvAP2 transcript (10). Alleles at this locus are assigned locus symbols: The Zeo1 mutants exhibit the most extreme phenotypes, the Zeo2 variants have intermediate phenotypes, and the Zeo3 variants 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 (BGS614) and Zeo3 (BGS742) groups (10).

Erectoides-52 = ert-52 (6, 7).
Erectoides-r = Ert-r (12).
"Kurz und dicht" = Knd (15, 18).
Cleistogamy = Cly (9, 10, 13, 17).
Hordeum vulgare APELATA2 (AP2)-like transcription factor = HvAP2 (10).

Monofactorial incomplete dominant (6, 14).
Located in chromosome 2HL (9, 11,17); Zeo1.a is about 9.2 cM distal from the lig1 (liguleless 1) locus (11); Zeo1.a is about 7.3 cM distal from RFLP marker cnx1 in 2H bin 13 (1); the Ert-r.52 allele in Bowman backcross-derived line BW322 is associated with SNP markers 2_0715 to 1_0551 (positions 213.08 to 221.70 cM) in 2H bin 13 (2); the Zeo1.a allele in BW937 is associated with SNP markers 2_0715 to 2_1453 (positions 213.08 to 245.71 cM) in 2H bin 13/14 (2); the Zeo1.b allele in BW938 is associated with SNP markers 1_1486 to 2_0590 (positions 202.70 to 218.47) in 2H bin 13 (2), the HvAP2 locus is near marker BOPA2_12_10579 (10), in 2H bin 13.

The name zeocriton (little barley) has been historically applied to cultivars with very short rachis internodes and a pyramid shape. This name and the locus symbol Zeo1 were applied to induced mutants having a similar phenotype (18). Homozygous Zeo1 plants have shorter culms (short peduncle), very compact spikes, large outer glumes with long awns, and reduced fertility. Plants heterozygous for the Zeo1 mutant have short culms, compact spikes, and wide kernels. (18). Generally, the spike emerges from the side of the sheath in homozygotes (5, 18). Although the name zeocriton is used for this gene, this gene is not from Spratt, the dense ear type described by Engledow (3) or those described by Hayes and Harlan (8). Spikes of plants with the Ert-r.52 mutant are compact in heterozygotes and very compact in homozygotes, with rachis internode length values from 1.4 to 1.8 mm. Homozygotes are about 2/3 normal height with excellent vigor. The glumes associated with lateral spikelets are 3 to 4 times larger than normal. Lodicule size is reduced (14). Heterozygotes are intermediate in plant height, have slightly more lax spikes, and have normal glumes in lateral spikelets (14). GA3 treatment of plants as the flag leaf emerges decreases spike density (16). Plants in Bowman backcross-derived lines for Ert-r.52 (BW322), Zeo1.a (BW937), and Zeo1.b (BW938) are about 2/3 the height of Bowman. Rachis internodes are about 1/2 normal length (2.2 vs. 4.4 mm). Mutant plants head about two days later than Bowman; they have about 2 more kernels per spike and their grain yields are about 3/4 of those of Bowman (5). The BW938 (Zeo1.b) averaged one more fertile rachis node than Bowman (10). DNA sequencing showed that the Zeo1 mutants occur in a Hordeum vulgare APELATA2 (AP2)-like transcription factor, HvAP2 (10, 13). 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, 13). The Zeo1 mutants occur in the last intron of HvAP2, the binding site of Hv-miR172, and prevent cleavage of the HvAP2 mRNA (10, 13).

An X-ray induced mutant in Donaria (PI 161974) (12); a neutron induced mutant in Bonus (NGB 14657, PI 189763) (6).

Zeo1.a (Mut 2657, GSHO 1613) in Donaria (PI 161974) (15) has haplotype 4 in the HVAP2 gene (10); Zeo1.b, received as "Kurz und dicht" and placed in R.I. Wolfe's Multiple Dominant Marker Stock (GSHO 1614) (4, 18) has haplotype 1 (10); Ert-r.52 (NGB 112651, GSHO 492), -r.67 (NGB 112666) in Bonus (NGB 14657, PI 189763) (12) have haplotype 1 (10); Ert-r.329 (NGB 112844) in Foma (NGB 14659, CIho 11333) (14) has haplotype 1 (10); Ert-r.453 (NGB 112968) in Foma (12) has haplotype 2 (10). Other variants in the HvAP2 gene are assigned to the Zeo2 (BGS614) or Zeo3 (BGS742) groups (10).

Zeo1.a (GSHO 1613 in Donaria; Zeo1.a in Bowman (PI 483237)*5 (GSHO 1931), in Bowman*7 (BW937, NGB 22366); Zeo1.b from R.I. Wolfe's Multiple Dominant Marker Stock (GSHO 1614) in Bowman*9 (GSHO 1932, BW938, NGB 22367); Ert-r.52 (Zeo1.a) (GSHO 492, NGB 112651) in Bonus; Ert-r.52 in Bowman (PI 483237)*8 (GSHO 2123, BW322, NGB 22117).

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5. Franckowiak, J.D. (Unpublished).
6. Hagberg, A., Å. Gustafsson, and L. Ehrenberg. 1958. Sparsely contra densely ionizing radiations and the origin of erectoid mutants in barley. Hereditas 44:523-530.
7. Hagberg, A., G. Persson, and A. Wiberg. 1963. Induced mutations in the improvement of self-pollinated crops. p. 105-124. In E. Åkerberg and A. Hagberg (eds.) Recent Plant Breeding Research. Svalöf 1946-1961. Almqvist & Wiksell, Stockholm.
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11. Luna Villafaña, A., and J.D. Franckowiak. 1995. (Unpublished).
12 Lundqvist, U., and J.D. Franckowiak. 1997. BGS 332, Erectoides-r, Ert-r. Barley Genet. Newsl. 26:280.
13. Nair, S.K., N. Wang, Y. Turuspekov, M. Pourkheirandish, S. Sinsuwongwat, G. Chen, M. Sameri, A. Tagiri, I. Honda, Y. Watanabe, H. Kanamori, T. Wicker, N. Stein, Y. Nagamura, T. Matsumoto, and T. Komatsuda. 2010. Cleistogamous flowering in barley arises from the suppression of microRNA-guided HvAP2 mRNA cleavage. Proc. Natl. Acad. Sci. USA 107:490-495.
14. Persson, G., and A. Hagberg. 1969. Induced variation in a quantitative character in barley. Morphology and cytogenetics of erectoides mutants. Hereditas 61:115-178.
15. Scholz, F., and O. Lehmann. 1958. Die Gaterslebener Mutanten der Saatgerste in Beziehung zur Formenmannigfaltigkeit der Art Hordeum vulgare L.s.l. I. Kulturpflanze 6:123-166.
16. Stoy, V., and A. Hagberg. 1967. Effects of growth regulators on ear density mutants in barley. Hereditas 58:359-384.
17. Turuspekov, Y., Y. Mano, I. Honda, N. Kawada, T. Watanabe, and T. Komatsuda. 2004. Identification and mapping of cleistogamy genes in barley. Theor. Appl. Genet. 109:480-487.
18. Wolfe, R.I. (Unpublished).

J.D. Franckowiak and R.I. Wolfe. 1997. Barley Genet. Newsl. 26:120.
U. Lundqvist and J.D. Franckowiak. 1997. Barley Genet. Newsl. 26:280. as BGS 332, Erectoides-r, Ert-r.

J.D. Franckowiak. 2007. Barley Genet. Newsl. 37:209.
J.D. Franckowiak and U. Lundqvist. 2011. Barley Genet. Newsl. 41:89-90.
J.D. Franckowiak and U. Lundqvist. 2017. Barley Genet. Newsl. 47:63-64.