Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 5.37

Sequence variation at the dhn4 locus in wild and cultivated barley

S. GIULIANI*, M. MACCAFERRI*, S. SALVI*, R. TUBEROSA*, D.W. CHOI**, Y.J. CLOSE**

*) Department of Agroenviromental Science and Tecnology, University of Bologna, viale Fanin 44, 40127 Bologna, Italy

**) Department of Botany & Plant Science, University of California, Riverside, CA, 92521-0124, USA

drought tolerance, Hordeum, natural allelic variation

Dehydrins (LEA D11 proteins) are water-soluble lipid-associating proteins that accumulate during low-temperature or water deficit conditions, and play a role in freezing and drought-tolerance in plants. It has been suggested that DHNs act as stabilizers of membranes or proteins. DHNs exist as multi-gene families in plants. The most complete information about Dhn genes is in barley where until now 13 different classes have been identified and mapped on 5 chromosomes (Choi et al, 1999, TAG 98: 1234-1247). Dehydrins are characterized by an abundance of charged and polar amino acids, and contain consensus amino acid sequence domains termed Y-, S-, and K-segments. These conserved domains are pieced together in a consistent manner, interspersed by other lesser conserved and usually repeated domains (phi-segments) (Close 1996, Phys. Plantarum 97: 795-803).

Allelic differences in the protein-coding regions appear to derive mainly from duplications of entire phi-segments or single amino-acid substitutions, suggesting that polypeptide structural constraints have been a strong force in the evolution of DHN alleles.

We have attempted to explore natural allelic variation in cultivated barley Hordeum vulgare and its wild progenitor H. spontaneum at the Dhn4 locus, which encodes a major drought-induced and seed protein. In this study, we included accessions of H. spontaneum from a wide range of collection sites and cultivars of H. vulgare as a representative sample of barley germplasm cultivated in Europe and North America. DNA sequencing of Dhn4 showed three major types of allelic variation, two at the protein level and one regarding the intron. At the protein level, we found a variable number of phi-segments between the K₁ and K₂ domains, ranging from six to nine in total. The majority of the accession analysed shows a phi-7 structure in which two central domains are missing. Moreover, variable amino acids (AAs) or AA clusters have been identified at four different regions within the ORF. In H. spontaneum two very different intron classes have been identified. Interestingly, the genetic variation at Dhn4 appears non-randomly organized in the H. spontaneum germplasm, with the intron and exon variants combined in two haplotype classes (spanning the Dhn4 full lenght sequence); only one of these two haplotype classes has been found in H. vulgare. More rearrangements, with several haplotypes, have been observed in the phi segment array region. In total, seven haplotypes were found in the germplasm accession herein analysed. Excellent opportunities exists for developing high-throughput assays targeted to the relevant SNPs and other sequence polymorphisms of Dhn4.