BGS 31, Shrunken endosperm xenia 6, sex6

starch synthase IIa = ssIIa (6).

Monofactorial recessive (1).
Located in chromosome 7HS (8); sex6.h is located about 2.8 cM distal from the seg2 (shrunken endosperm genetic 2) locus (7); sex6.h is about 3.1 cM from the centromere (8); sex6.h is over 45.8 cM proximal from the Est5 (esterase 5) locus (8); sex6.h is about 4.4 cM from the breakpoint in translocation stock T1-5a (9); sex6.h is associated with SNP markers 1_1028 to 2_0485 (positions 72.84 to 84.79 cM) in 7H bin 07 of the Bowman backcrossed-derived line BW846 (2), in 7H bin 07.

After the soft dough stage, kernels develop a central depression in the center of the lemma side, which becomes progressively more distinct with maturity. The depression is similar in size to that produced by sex1 (shrunken endosperm xenia 1) mutants. The mutant has a xenia expression that permitting classification of kernels from heterozygous plants as normal or shrunken with an expected 3:1 ratio (3). Kernels of allelic mutants, M292 and M342 had a high amylose starch phenotype, 60 to 70% compared to 25% in normal barley (6). The starch synthase IIa (ssIIa) gene is a candidate gene altered by these mutations (6). Compared to Bowman, plants of the Bowman backcross-derived line for sex6.h, BW846, were about 10% shorter and headed about three days later. Kernel weights for BW846 were 2/3 to 3/4 of those for Bowman, 3.8 vs. 5.6 mg. Grain yields of BW846 were about 1/2 those recorded for Bowman (3). On a per kernel basis, grain from lines containing both the high amylose 1 (amo1, ssIIIa) mutant and the sex6 (ssIIa) mutant from the M292 synthesize significantly more amylose than wild-type lines and the sex6 mutants (5).

A spontaneous mutant in K6827 (an introduction from Turkey) (1).

sex6.h (GSHO 2476) in K6827 (MK6827) (1); M292 (Himalaya292) and M342 (Himalaya342) in Himalaya (CIho 1312) (5, 6).

sex6.h (GSHO 2476) in K6827; sex6.h in Bowman (PI 483237)*6 GSHO 3425); sex6.h in Bowman*7 (BW846, NGB 22283), sex6.h in NFC Triple (Syngenta Seeds Ltd., Market Rasen, UK)*3 (4).

1. Biyashev, R.M., V.P. Netsvetaev, and A.A. Sozinov. 1986. Genetic control of some morphological markers for qualitative and biochemical characters and location of three genetic factors on chromosomes 1 and 5 of barley, Hordeum vulgare L. Sov. Genet. 22:226-232. (Translation of Genetika 22:296-303).
2. Druka, A., J. Franckowiak, U. Lundqvist, N. Bonar, J. Alexander, K. Houston, S. Radovic, F. Shahinnia, V. Vendramin, M. Morgante, N. Stein, and R. Waugh. 2011. Genetic dissection of barley morphology and development. Plant Physiol. 155:617-627.
3. Franckowiak, J.D. (Unpublished).
4. Howell, A., F. Leigh, R. Bates, N. Gosman, K. Trafford, W. Powell, A.M. Smith, and A. Greenland. 2014. Rapid marker-assisted development of advanced recombinant lines from barley starch mutants. Mol. Breed. 33:243-248.
5. Li, Z., D. Li, Dehong; X. Du, H. Wang, O. Larroque, C.L.D. Jenkins, S.A. Jobling, and M.K. Morell. 2011. The barley amo1 locus is tightly linked to the starch synthase IIIa gene and negatively regulates expression of granule-bound starch synthetic genes. J. Exp. Bot. 62:5217-5231.
6. Morell, M.K., B. Kosar-Hashemi, M. Cmiel, M.S. Samuel, P. Chandler, S. Rahman, A. Buléon, I.A. Batey, and Z. Li. 2003. Barley sex6 mutants lack starch synthase IIa activity and contain a starch with novel properties. Plant J. 34:173-185.
7. Netsvetaev, V.P. 1990. [Location of a shrunken endosperm gene, sex 6, in barley.] Nauchno-Tekh. Bull' VSGI, Odessa. No. 1 (75):31-35. [In Russian.]
8. Netsvetaev, V.P. 1992. [Use of double ditelosomics for gene location in barley.] Cytology and Genetics (Kiev) 26:26-30. [In Russian.]
9. Netsvetaev, V.P., and I.S. Krestinkov. 1993. Chromosomal position of the superoxide dismutase locus, Sod1 (=Sod B), in barley. Barley Genet. Newsl.22:44-45.

J.D. Franckowiak. 1997. Barley Genet. Newsl. 26:80.

Revised:J.D. Franckowiak. 2015. Barley Genet. Newsl. 45:86-87.