Caleosins: Ca2+-binding proteins associated with lipid bodies

We have previously identified a rice gene encoding a 27 kDa protein with a single Ca2+-binding EF-hand and a putative membrane anchor. We report here similar genes termed caleosins, CLO, in other plants and fungi; they compri se a multigene family of at least five members in Arabidopsis (AtClo1-5). N orthern hybridization demonstrated that AtClo2-4 mRNAs levels were low in v arious tissues, while AtClo1 mRNA levels were high in developing embryos an d mature seeds. Analysis of transgenic Arabidopsis plants expressing the GU S reporter under control of the AtClo1 promoter showed strong levels of exp ression in developing embryos and also in root tip cells. Antibodies raised against AtCLO1 were used to detect caleosin in cellular fractions of Arabi dopsis and rapeseed. This indicated that caleosins are a novel class of lip id body proteins, which may also be associated with an ER subdomain.