| Description |
We identified the Rbz gene by Ds tagging (Sundaresan et al. 1995 Genes Develop. 9, 1797-810) and by rbz complementation with a full cDNA (unpublished). The recessive rbz knockout is slow to green (wt. vs. rbz), similar to cue (Li et al. 1995 Plant Cell 7, 1599-1610) or yellow heart (Redei 1965 Arab. Info. Serv.) mutants, although crosses show it is not allelic to those on the same chromosome 5. rbz epithelium is normal but the leaves collapse due to retarded chloroplast and palisade cell development. The 80kD RBZ protein has Cys4 zinc fingers with a consensus specific to cytoplasmic nucleoporins which bind Ran (Nakielny et al. 1999 EMBO J. 18, 1982-1995; Haizel et al. 1997 Plant J. 11, 93-103). RBZ also contains three novel repeats, and proline-rich regions similar to SH3 interaction domains (Nguyen et al., 1998 Science 282, 2088-2092). We identified three proteins by yeast 2-hybrid screening and in vitro binding assays which specifically interact with RBZ: 1) IFAP, a coiled-coil, intermediate filament protein which may be nuclear membrane associated (AF004556; McNulty & Saunders 1992 J. Cell Sci. 103, 407-414); 2) another coiled-coil protein (MXM12.P4) similar to a yeast intermediate filament protein involved in intracellular protein transport (P25386); and 3) neoxanthin cleavage enzyme (Z93765), a chloroplast-targeted enzyme. Such RBZ and partner features, as well as the rbz phenotype, suggest that RBZ is involved in nuclear to chloroplast trafficking or signaling via novel cytoskeletal components (Jarvis et al. 1998 Science 282, 100-03). Initial northerns indicate that chalcone synthase and RBCS are over-expressed 5 fold in rbz vs. Ler wt., suggestive of an aberration in light signalling (Mayer et al. 1996 Plant Cell 8, 1951-59). Microarray analysis of rbz vs. wt. would provide a profile of global gene expression in the mutant and lead to a better understanding of RBZ function. We have already prepared 5ug mRNA from whole three week old plantlets of Ler wt. and rbz using TRIzol/Qiagen Oligotex, a protocol we have used for other mutant microarray analyses at Monsanto. |
