Isolation and characterization of a drought-induced soybean cDNA encoding a D95 family late-embryogenesis-abundant protein.

LEA proteins represent severa1 families of proteins that accumulate to high levels in maturing seeds. The expression of these proteins is under developmental control, but they may also be expressed in dissected embryos exposed to exogenous ABA (Hughes and Galau, 1991). Many Leu genes are also expressed in vegetative tissues exposed to exogenous ABA as well as water, osmotic, and low-temperature stress (Bray, 1993). The majority of LEA proteins are hydrophilic, display a preponderance of specific amino acids, and are localized to the cytoplasm (Dure, 1993b) and the nucleus (Goday et al., 1994). LEA proteins have been proposed to participate in various protective roles during times of severe desiccation stress. Their presence in young wheat seedlings has also been correlated with desiccation tolerance (Reid and Walker-Simmons, 1993). Severa1 families of LEA proteins (D19 and D113) are predicted to bind water. This waterbinding capaaty is thought to prevent complete desiccation of tissues and thereby preserve protein and membrane integrity (Dure, 1993b). Another diverse LEA protein family (D11) may function to preserve protein structure through the renaturation of unfolded proteins (Dure, 1993a). Other LEA protein families (D7 and D29) may be involved in sequestering ions that accumulate in desiccating tissues (Dure, 1993b). Here we report the isolation and expression of a conserved cDNA clone encoding a LEA protein from water-stressed soybean leaves belonging to the D95 family. The predicted soybean Lea gene product shares 78.8 and 68.2% amino acid identity with the predicted cotton Leal4 (D95) (Galau et al., 1993) and resurrection plant pcC27-45 gene products, respectively (Piatkowski et al., 1990). This family of proteins shares no amino acid sequence similarity with other LEA proteins. In contrast to other LEA proteins, which are very hydrophilic, D95 LEA proteins display a slightly hydropathic character throughout the length of the protein (Galau et al., 1993). The N-terminal40 amino acids of the soybean LEA14 homolog form a predicted mildly hydrophilic a helix with the remainder of the protein evenly divided between hydrophobic and hydrophilic regions (Table I). Helical wheel analy-