Production of multiple plant hormones from a single polyprotein precursor

Some animal and yeast hormone genes produce prohormone polypeptides that ar e proteolytically processed to produce multiple copies of hormones with the same or different functions(1). In plants, four polypeptides have been ide ntified that can be classed as hormones(2-5) (intercellular chemical messen gers(6)) but none are known to be produced as multiple copies from a single precursor. Here we describe a polyprotein hormone precursor, present in to bacco plants, that gives rise to two polypeptide hormones, as often found i n animals and yeast. The tobacco polypeptides activate the synthesis of def ensive proteinase-inhibitor proteins in a manner similar to that of systemi n, an 18-amino-acid polypeptide found in tomato plants(2). The two tobacco polypeptides are derived from each end of a 165-amino-acid precursor that b ears no homology to tomato prosystemin. The data show that structurally div erse polypeptide hormones in different plant species can serve similar sign alling roles, a condition not found in animals or yeast.