Molecular characterization of cDNAs encoding G protein alpha and beta subunits and study of their temporal and spatial expression patterns in Nicotiana plumbaginifolia Viv.

We isolated cDNA sequences encoding alpha and beta subunits of potential G proteins from a cDNA library prepared from somatic embryos of Nicotiana plu mbaginifolia Viv. at early developmental stages. The predicted NPGPA1 and N PGPB1 gene products are 75-98% identical to the known respective plant alph a and beta subunits. Southern hybridizations indicate that NPGPA1 is probab ly a single-copy gene, whereas at least two copies of NPGPB1 exist in the N . plumbaginifolia genome. Northern analyses reveal that both NPGPA1 and NPG PB1 mRNA are expressed in all embryogenic stages and plant tissues examined and their expression is obviously regulated by the plant hormone auxin. Im munohistological localization of NPGP alpha 1 and NPGP beta 1 preferentiall y on plasma and endoplasmic reticulum membranes and their immunochemical de tection exclusively in microsomal cell fractions implicate membrane associa tion of both proteins. The temporal and spatial expression patterns of NPGP A1 and NPGPB1 show conformity as well as differences. This could account fo r not only cooperative, but also individual activities of both subunits dur ing embryogenesis and plant development. (C) 2000 Elsevier Science B.V. All rights reserved.