A wide range of molecules are transported across membranes by the ATP binding cassette (ABC) transporters. Plants possess a collection of ABC proteins bearing similarities to the components of prokaryotic multi subunit ABC transporters, designed as ABC group I. However the functions of most of them are not well understood. Here, we characterized a naturally occurring rice mutant that exhibited albino phenotype under continuous rainy days in the field, but gradually recovered to normal green after the rainy season. Molecular and genetic analyses revealed that the phenotypes were caused by a mutation in the OsABCI8 that encoded a member of the ABCI family. Subcellular localization demonstrated that OsABCI8 is a chloroplast ABC transporter. Expression of OsABCI8 is significantly enhanced in rainy days compared to sunny days. Besides defects in chloroplast development and chlorophyll biosynthesis, the mutant phenotype is accompanied by a higher accumulation of iron, suggesting that OsABCI8 is involved in iron transportation and/or homeostasis in rice. Our results demonstrate that OsABCI8 represents a conserved ABCI protein involved in transition metals transportation and/or homeostasis and suggest an important role of the plastid-localized OsABCI8 for chloroplast development.
Lignin is a major constituent of plant cell walls and indispensable to the normal growth of a plant. However, the presence of lignin complicates the structure of the plant cell walls and negatively influences pulping industry, lignocellulose utilization as well as forage properties. Cinnamyl alcohol dehydrogenase (CAD), a key enzyme involved in lignin biosynthesis, catalyses the last step in monolignol synthesis and has a major role in genetic regulation of lignin production. In the present study, a 1 342-bp cDNA fragment of CAD gene, named PpCAD, was isolated from Pennisetum purpureum using strategies of homologous clone and rapid amplification of cDNA end. It was translated into an intact protein sequence including 366 amino acid residues by ORF Finder. The genomic full-length DNA of PpCAD was a 3 738-bp sequence containing four exons and three introns, among which the 114-bp exon was considered to be a conserved region compared with other CADs. Basic bioinformatic analysis presumed that the PpCAD was a nonsecretory and hydrophobic protein with five possible transmembrane helices. The phylogenetic analysis indicated that the PpCAD belonged to the class of bona fide CADs involved in lignin synthesis and it showed a high similarity (nearly 90%) with CAD protein sequences of Sorghum bicolor, Panicum virgatum and Zea mays in Gramineae. Furthere, PpCAD amino acid sequence was demonstrated to have some conserved motifs such as Zn-binding site, Zn-catalytic centre and NADP(H) binding domain after aligning with other bona fide CADs. Three-dimensional homology modelling of PpCAD showed that the protein had some exclusive features of bona fide CADs.
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