Regulation and evolution of the patatin multigene family : suggestions of combinatorial interactions directing tissue-specific gene expression

Abstract

While much has been written about the evolution of new tissues or organs, little is known about the origin of the regulatory elements that direct gene expression in new structures. Questions also arise about how new regulatory elements are integrated into the complex physiology of new tissues. To examine these questions, the patatin multigene family was used as a model system. Patatin is a family of lipid acyl hydrolases that accounts for 30-40% of the total protein in potato tubers. The Class-I genes, which produce the majority of the patatin protein in tubers, can also be induced to express at high levels in stems and leaves by 0.2 -0.3 M sucrose. However, under normal conditions, they are almost totally tuber-specific. To examine how "tuber-specific" genes could have evolved from regulatory elements in non-tuberizing species, the expression of the endogenous patatin genes in tomato and tobacco were compared to that of potato Class-I patatin promoters using transgenic plants. Patatin promoters were also isolated and characterized from tobacco and evolutionarily divergent species of wild potato. These promoters contain sequences characteristic of both the Class-I and Class-II patatin genes. However, their patterns of expression are unlike those of any previously reported patatin genes. They were neither sucrose inducible nor tuber-specific and were wound-inducible, unlike potato Class-I patatin genes which are turned off by wounding. Because the major soybean vegetative storage protein (VSP) serves similar roles in soybeans to that served by patatin in potatoes, vsp promoter expression in transgenic potato plants was also examined. Although vsp is normally expressed in soybean leaves, it was tuber-specific when introduced into potato plants. Like Class-I patatin, vsp could be induced to express in leaves by sucrose, but unlike patatin, vsp could also be induced by methyl jasmonate, systemin and oligourinides...