SPECIFIC AND DIFFERENT EXPRESSION PATTERNS OF TWO MEMBERS OF THE LEAF THIONIN MULTIGENE FAMILY OF BARLEY IN TRANSGENIC TOBACCO

摘要

Thionins are cysteine-rich, basic, and toxic proteins that are assumed to be involved in the defense against pathogens. Barley (Hordeum vulgare L. cv. Carina) contains a large gene family coding for leaf-specific thionins that comprises more than 50 genes per haploid genome. How the expression of these variants is regulated was not known. To address this question, we have cloned 2 of these thionin genes, BTH6 and BTH7, each belonging to one of 2 subgroups, and analysed their sequences. Both code for typical leaf thionin proteins. Their promoter regions have an identity of about 40% except for a region of 90 bp in the downstream region which has an identity of 80%. As reflected by these sequence differences, both promoters behave differently when placed in front of the uidA gene and analysed in transgenic tobacco plants. Whereas the BTH6 promoter is constitutively expressed in most tissues of transgenic tobacco plants except the roots, the BTH7 promoter is only active in the vascular strands of the stem and older leaves. The BTH6 promoter is highly active in the epidermis and in xylem elements whereas the BTH7 promoter shows very high activity in phloem elements. In addition, both promoters are differently regulated by light. The BTH7 promoter is only active in the light. The BTH6 promoter shows a differential regulation in seedlings, being active in the hypocotyl in darkness but not in the cotyledons and vice versa in the light. Our results indicate that the expression of the barley leaf thionin multigene family is regulated differentially at the transcriptional level. [References: 45]