The Low Molecular Weight Heat Shock Proteins of Soybean Seedlings

Abstract

The heat shock (HS) response has been studied extensively for about 30 years since the discovery of the phenomenon in Drosophila in the early 1960s; studies in plants have been restricted generally to less than 15 years. Heat shock is the subject of numerous reviews in recent years (e.g. Craig, 1985; Kimpel and Key, 1985a; Key et al., 1985a; 1985b; Lindquist, 1986; Lindquist and Craig, 1988; Nagao et al., 1986; Key et al., 1987a; 1987b; Nagao and Key, 1989; Nagao et al., 1990; Neumann et al., 1989; Vierling, 1991; Gurley and Key, 1991). Since various aspects of the HS response in a number of plant systems are covered in this volume, the comments of this contribution will focus on our work on the low molecular weight (LMW) heat shock proteins (hsps) of soybean seedlings, much of which is detailed in some of the reviews cited above, with emphasis on expression of the HS genes encoding hsps, and some properties of those proteins, in the 15 to 27 kD range. This relates to a rather unique feature of HS in plants in that most plants synthesize a large number of LMW hsps, and some of these are generally the most abundant hsps expressed in plants. Most other eukaryotes, in contrast, synthesize a limited number of LMW hsps, and these are generally much less abundant than the 70 kD and 83/90 kD hsps, with hsp70 proteins often representing the majority of hsp synthesis in many organisms. Plants synthesize a complement of hsps in the 60 kD, 70 kD, 83/90 kD, and 104/110 kD MW range which appear to be homologs of the corresponding hsps of other eukaryotes.