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Molecular Plant 2009 2(3):430-441; doi:10.1093/mp/ssp025
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© The Author 2009. Published by the Molecular Plant Shanghai Editorial Office in association with Oxford University Press on behalf of CSPP and IPPE, SIBS, CAS.

The Level of Expression of Thioredoxin is Linked to Fundamental Properties and Applications of Wheat Seeds

Yong-Chun Lia,2, Jiang-Ping Rena,2, Myeong-Je Chob, Su-Mei Zhoua, Yong-Bum Kimb, Hong-Xiang Guoa, Joshua H. Wongb, Hong-Bin Niua, Hyun-Kyung Kimb, Susumu Morigasakib, Peggy G. Lemauxb, Oscar L. Frickc, Jun Yina,1 and Bob B. Buchananb,1

a National Engineering Research Centre for Wheat, Henan Agricultural University, Zhengzhou 450002, China
b Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720, USA
c Department of Pediatrics, School of Medicine, University of California, San Francisco, CA 94143, USA

1 To whom correspondence should be addressed. Buchanan: E-mail view{at}nature.berkeley.edu, tel. +1 510 642-3590. Yin: E-mail junyin57{at}yahoo.com.cn, tel. +86 371 63558203.

Work with cereals (barley and wheat) and a legume (Medicago truncatula) has established thioredoxin h (Trx h) as a central regulatory protein of seeds. Trx h acts by reducing disulfide (S–S) groups of diverse seed proteins (storage proteins, enzymes, and enzyme inhibitors), thereby facilitating germination. Early in vitro protein studies were complemented with experiments in which barley seeds with Trx h overexpressed in the endosperm showed accelerated germination and early or enhanced expression of associated enzymes ({alpha}-amylase and pullulanase). The current study extends the transgenic work to wheat. Two approaches were followed to alter the expression of Trx h genes in the endosperm: (1) a hordein promoter and its protein body targeting sequence led to overexpression of Trx h5, and (2) an antisense construct of Trx h9 resulted in cytosolic underexpression of that gene (Arabidopsis designation). Underexpression of Trx h9 led to effects opposite to those observed for overexpression Trx h5 in barley—retardation of germination and delayed or reduced expression of associated enzymes. Similar enzyme changes were observed in developing seeds. The wheat lines with underexpressed Trx showed delayed preharvest sprouting when grown in the greenhouse or field without a decrease in final yield. Wheat with overexpressed Trx h5 showed changes commensurate with earlier in vitro work: increased solubility of disulfide proteins and lower allergenicity of the gliadin fraction. The results are further evidence that the level of Trx h in cereal endosperm determines fundamental properties as well as potential applications of the seed.

Key Words: metabolic regulation • molecular physiology • seed biology • preharvest sprouting • seed germination • thioredoxin h • wheat allergenicity

2 These authors made equal contributions to this work.


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