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GERMPLASM

Registration of a Hexaploid Wheat Translocation Line Carrying a Short Segment of Chromosome 5A^m including Softness Genes Pina and Pinb from Triticum monococcum

^a Instituto de Recursos Biológicos, INTA Castelar (1686) Hurlingham, Buenos Aires, Argentina
^b Dep. of Plant Sciences, Univ. of California, Davis, CA 95616-8780. This project was supported by the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service (CSREES) grant number 2006-55606-16629, and by Argentinean grants BID 1728/OC-AR PID 234 and PICTO 08-12948

^* Corresponding author (jdubcovsky{at}ucdavis.edu).

ABSTRACT

Translocation line T5A^mS-5AS·5AL R#45 (Reg. No. GP-839, PI 651012) carries the distal region of Triticum monococcum L. chromosome 5A^mS translocated into the 5AS chromosome of T. aestivum L. cultivar Chinese Spring. This translocation line was developed in collaboration with the Instituto de Recursos Biológicos, INTA, Argentina, and the University of California, Davis, CA. The distal T. monococcum 5A^mS segment in T5A^mS-5AS·5AL R#45 is approximately 8 cM long and carries the active softness genes Pina and Pinb in the genetic background of Chinese Spring. This translocation replaced the deleted Pina and Pinb puroindoline genes from T. aestivum by the functional orthologs from T. monococcum, significantly reducing the hardness of the grain. Translocation line T5A^mS-5AS·5AL R#45 has a shorter segment of T. monococcum chromosome 5A^m relative to previous translocations, minimizing linkage drag and the probability of negative effects associated with the introgression of alien genes.

Abbreviations: CS, Chinese Spring

Translocation line T5A^mS-5AS·5AL R#45 (Reg. No. GP-839, PI 651012) was developed by the Instituto de Recursos Biológicos, INTA, Argentina in collaboration with the University of California, Davis, CA. This line carries a distal segment of Triticum monococcum L. chromosome 5A^mS translocated to the 5AS chromosome of T. aestivum L. cultivar Chinese Spring.

The translocated 5A^mS segment from T. monococcum is approximately 8 cM long and carries the active puroindoline genes Pina and Pinb in the genetic background of Chinese Spring. The objective of this translocation was to replace the deleted puroindoline genes from T. aestivum chromosome 5A by the functional orthologs present in T. monococcum chromosome 5A^m. The puroindoline genes are responsible for the softness of the grain, and the addition of functional puroindoline genes was expected to reduce the hardness of the grain.

Triticum monococcum chromosomes do not recombine well with T. aestivum chromosomes (Dubcovsky et al., 1995; Luo et al., 2000), and therefore translocated 5A^m segments block or significantly reduce recombination in those regions. We induced homeologous recombination by the ph1b mutation and reduced the length of the translocated 5A^m chromosome segment from 40 to 8 cM in T5A^mS-5AS·5AL R#45. This shorter segment is expected to reduce linkage drag and the risk of negative effects associated with the introduction of other alien genes.

Methods

Translocation line T5A^mS-5AS·5AL R#45 was derived from a backcross population where 5A/5A^m homeologous recombination was induced by the ph1b mutation. The backcross population involved an F₁ between the Chinese Spring (CS) line carrying the ph1b mutation (Sears 1977) and the CS 5A/5A^m recombinant substitution line number 25, which carries a 40-cM distal chromosome segment from T. monococcum (Luo et al., 2000) including the Ha locus (Pina-A^m1, Pinb-A^m1, and GSP-A^m1). This F₁ was backcrossed to CS.

Molecular markers were used to construct a genetic map for the 5AS/5A^mS recombinant lines and to select the lines with the shortest 5A^m segment including the Hardness locus from T. monococcum. Recombinant 45 (R#45) has a distal translocation (approximately 8 cM) with a recombination event between the XBggp and XBG606847 loci (Bonafede et al., 2007). This translocation replaced the deleted Pina and Pinb puroindoline genes from T. aestivum 5AS arm by the functional orthologs from T. monococcum. The recombinant line was self-pollinated, and plants homozygous for the T5A^mS-5AS·5AL translocation and homozygous for the wild-type Ph1b allele were selected with molecular markers.

Characteristics

Grain hardness was measured in 12 plants homozygous for the T5A^mS-5AS·5AL R#45 line and 12 sister lines without the T. monococcum translocation grown in a completely randomized design in the greenhouse. Hardness was evaluated using 300 kernels per line and a Single Kernel Characterization System Model 4100 (Perten Instruments, Segeltorp, Sweden). Seeds from R#45 (scores 30.1 ± 0.7) were significantly softer (P < 0.0001) than those from Chinese Spring (53.2 ± 0.9).

This result parallels the effect of the larger T. monococcum 5A^m segment on grain texture described previously (Tranquilli et al., 2002) and demonstrates that the genes affecting hardness are still present in the reduced 5A^m segment. Therefore, the shorter T. monococcum segment present in T5A^mS-5AS·5AL can be a useful tool to reduce grain hardness in common wheat.

A high-throughput codominant marker for the XBggp locus, which is tightly linked to the Pin genes, can be used to select the T. monococcum Ha allele in marker assisted selection programs. However, it is worth to check the final homozygous lines with the T. monococcum Pin markers as a final confirmation for the transfer of the genes responsible for softer grains (Bonafede et al., 2007).

Availability

Seed samples of the stabilized R#45 line (homozygous for the Ph gene and T. monococcum Ha locus) have been deposited in the USDA-ARS National Small Grain Collection P.O. Box 307, Aberdeen, ID 83210, USA, and in the INTA Germplasm Bank, Castelar, Argentina. Small quantities can be obtained for research and breeding purposes from the curator of the National Small Grain Collection or from the senior author.

Footnotes

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Received for publication September 13, 2007.

References

• Bonafede, M., L. Kong, G. Tranquilli, H. Ohm, and J. Dubcovsky. 2007. Reduction of a Triticum monococcum chromosome segment carrying the softness genes Pina and Pinb translocated to bread wheat. Crop Sci. 47:821–826.[Abstract/Free Full Text]
• Dubcovsky, J., M.C. Luo, and J. Dvoák. 1995. Differentiation between homoeologous chromosomes 1A of wheat and 1A^m of Triticum monococcum and its recognition by the wheat Ph1 locus. Proc. Natl. Acad. Sci. USA 92:6645–6649.[Abstract/Free Full Text]
• Luo, M.-C., Z.L. Yang, R.S. Kota, and J. Dvoák. 2000. Recombination of chromosomes 3Am and 5Am of Triticum monococcum with homoeologous chromosomes 3A and 5A of wheat: The distribution of recombination across chromosomes. Genetics 154:1301–1308.[Abstract/Free Full Text]
• Sears, E.R. 1977. An induced mutant with homoeologous pairing in wheat. Can. J. Genet. Cytol. 19:585–593.
• Tranquilli, G., J. Heaton, O. Chicaiza, and J. Dubcovsky. 2002. Substitutions and deletions of genes related to grain hardness in wheat and their effect on grain texture. Crop Sci. 42:1812–1817.[Abstract/Free Full Text]

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