Gene note. Isolation of an Arabidopsis thaliana cDNA encoding a pleckstrin homology domain protein, a putative homologue of human pleckstrin

Screening of an Arabidopsis cDNA library allowed the isolation of a cDNA encoding a pleckstrin homology (PH) domain protein, AtPH1, which consists of one PH domain with a short N-terminal extension. According to its structural features, AtPH1 is proposed to be a plant homologue of human pleckstrin. Northern blot analysis indicated that the AtPH1 gene was expressed constitutively in all tissues examined, with variation in the levels. The presence of a plant pleckstrin homologue offers new insights into the biological function of the PH domain in plant signalling.     

Evaluation of a cDNA scanning method concerning the fidelity and efficiency of cDNA selection using the YAC CIC3B1-S region of Arabidopsis thaliana chromosome 5.

We previously reported a cDNA selection method using DNA latex particles to identify expressed genes in specific regions of genomes and named this cDNA scanning method (Hayashida et al., 1995 Gene 155 161). We applied the cDNA scanning method to the YAC CIC3B1-S DNA on Arabidopsis thaliana chromosome 5, and constructed a region-specific sublibrary in which cDNAs for genes on the YAC CIC3B1-S DNA were concentrated. We isolated 545 cDNA clones from the sublibrary, and determined partial sequence of them to produce expressed sequence tags (ESTs) derived from the YAC region. In total, 74 nonredundant groups of cDNAs were obtained from 545 cDNA clones. Forty-seven percent of these EST clones had significant homology to functional proteins such as protein kinases, LON protease, nucleic acid binding protein and chloride channel protein. We compared the cDNA sequences isolated by the cDNA scanning method to the Arabidopsis genomic sequence corresponding to the YAC CIC3B1-S region, and found that 69% of the selected cDNAs are located in the region. We discuss the fidelity and efficiency of the cDNA scanning method for cloning region-specific cDNAs and its useful application in positional cloning.     

A nuclear gene, erd1, encoding a chloroplast-targeted Clp protease regulatory subunit homolog is not only induced by water stress but also developmentally up-regulated during senescence in Arabidopsis thaliana

A cDNA, ERD1, isolated from one-hour-dehydrated plants of Arabidopsis thaliana L. encodes a putative protein that is similar to the regulatory ATPase subunit (ClpA) of the Clp protease and contains a putative chloroplast-targeting transit-peptide at the N-terminus. A chimeric gene with the putative plastid-targeting sequence of the erd1 gene fused to the synthetic green-fluorescent protein (sGFP) gene was constructed and introduced into Arabidopsis protoplasts. The N-terminal region of the ERD1 protein directed the sGFP protein into the plastids of the protoplasts, and functioned as a transit peptide. Northern blot analysis indicated that expression of the erd1 gene was induced not only by water stress, such as dehydration and high salinity, but also by natural senescence and dark-induced etiolation. The erd1 gene was not strongly induced by exogenous abscisic acid. A chimeric gene with the 0.9 kb promoter region of the erd1 gene fused to the β-glucuronidase (GUS) reporter gene was constructed, and tobacco plants transformed with the construct. The GUS reporter gene driven by the erd1 promoter was induced by dehydration and high salt stress at significant levels in the transgenic plants. The GUS gene was strongly expressed in older leaves without dehydration, and was induced by dark-induced etiolation. Furthermore, GUS activity was reduced by cytokinin treatment during dark-induced etiolation. These results indicate that expression of the erd1 gene is developmentally up-regulated by senescence as well as by water stress.