PLANT METALLOTHIONEINS: PUTATIVE FUNCTIONS IDENTIFIED BY PROMOTER ANALYSIS IN SILICO

摘要

Metallothioneins are low-molecular-weight proteins capable of covalently binding heavy metal ions due to thepresence of many cysteine residues in their sequences. We analyzed the predicted amino acid sequences of 19metallothionein (7 from Arabidopsis thaliana and 12 from Oryza sativa) and their promoter sequences in sil-ico in order to determine the potential regulatory cis-elements present in the promoters of metallothionein genes,from which it is possible to determine the putative functions of these genes. The PlantCARE and PLACE data-bases provided information about the putative regulatory elements in the metallothionein promoters. Metalresponse element sequences were found in the promoters of eleven O. sativa and two Arabidopsis metallo-thionein genes. Copper response elements were identified in both model plants, usually in many copies, partic-ularly in O. sativa. Both the high cysteine content and the presence of metal response motifs in the promoterssupport the suggestion that metallothioneins play a key role in metal detoxification. The most common putativeelement in the analyzed promoters was CIRCADIAN, which was present in five A. thaliana and eight O. sativasequences. The methyl jasmonate response sequence, root-specific expression element and drought responseelement were found only in O. sativa metallothioneins. Light and low temperature response elements, biotic andabiotic stress elements, an abscisic acid-responsive element and an ethylene-responsive element occur in select-ed metallothionein promoters of both species. A few promoters have putative organ- and cell-specific regulatoryelements. The presence of many different motifs in the promoters of the Arabidopsis and O. sativa genes impliesthat metallothioneins are general stress response proteins with many important functions in plants, includingregulation of their normal development and adaptation to changing environmental conditions