THE ANTIRRHINUM ERG GENE ENCODES A PROTEIN RELATED TO BACTERIAL SMALLGTPASES AND IS REQUIRED FOR EMBRYONIC VIABILITY

Small GTPases have diverse roles in animals and yeast, including signa l transduction, regulation of secretion, organisation of the cytoskele ton, and control of cell division. Similar GTPases have also been foun d in bacteria, such as the Escherichia coli GTPase ERA, which is invol ved in regulating metabolism and cell division [1,2], Many small GTPas es have been cloned from plants but their functional analysis has larg ely been limited to complementation of mutations in corresponding yeas t genes, and antisense experiments which have implicated these protein s in processes such as root nodulation [3,4]. No mutations in plant GT Pases have been reported, and thus their true importance in plant grow th and development is unknown. Here we report the isolation of a gene from Antirrhinum majus encoding a protein from an entirely novel class of eukaryotic GTPases showing strongest similarity to the prokaryotic protein ERA, We have named this gene ERG (for ERA-related GTPase), Th e ERG gene is expressed in dividing or metabolically active cells. We generated a deletion allele of ERG by site-selected transposon mutagen esis and have shown that seeds containing embryos and endosperm homozy gous for this deletion arrest soon after fertilisation. We conclude th at ERG has a crucial role in plant growth and development, possibly by influencing mitochondrial division.