A Maize cDNA Encoding a Type II Chlorophyll a/b-Binding Protein of Photosystem II

In higher plants, the CAB proteins are components of the antenna complexes associated with PSI and PSII in the chloroplast thylakoid membranes. They are encoded by a nuclear multigene family. Members of this family have been extensively characterized and categorized in 1 O recognizable types by deduced amino acid sequence comparison (Jansson et al., 1992). Six different protein types are associated with the antenna of PSII, divided into the major LHCII and the minor complexes CP29, CP26, and CP24 (Jansson et al., 1992). LHCII is composed of two major polypeptides (LHCII type I and type 11) and one minor polypeptide (LHCII type 111) (Jansson et al., 1992). LHCII type I and type I1 proteins are the most closely related proteins of the CAB family and share on average 85% homology (Jansson et al., 1992). In maize Zea mays), a11 the CAB genes that have been isolated code for LHCII type I polypeptides (Sullivan et al., 1989; Viret et al., 1990; Bansal et al., 1992; Becker et al., 1992). Here, we report the isolation and expression of a maize cDNA encoding an LHCII type 11 polypeptide. A cDNA library of maize seedlings in Xgtl 1 was screened with polyclonal antibodies against Chlamydomonas CAB polypeptides (Houlné and Schantz, 1987). This led to the isolation, subcloning in Bluescript KS+ plasmid (Stratagene, La Jolla, CA), and complete sequencing of a 1126-bp ECORI fragment that contains a 780-bp coding region for a maize CAB polypeptide (Table I). Hybridization studies and sequence comparisons do not identify this gene with one of the eight maize cDNAs characterized previously (Sheen and Bogorad, 1986; Sullivan et al., 1989; Viet et al., 1990; Bansal et al., 1992; Becker et al., 1992). Amino acid sequence comparison of this new clone with tomato LHCII CAB polypeptides of three different types and one maize LHCII type I CAB polypeptide reveals that it encodes an LHCII type I1 CAB. Its putative mature polypeptide shares 92,82, and 75%, respectively, sequence homology with the tomato LHCII type I1 (Pichersky et al., 1987), type I (Pichersky et al., 1985), and type 111 (Schwartz et al., 1991) proteins, and 81% with the maize LHCII type I protein (Viret et al., 1990). Its putative