Abstract
Guanylate kinase (Gmk) is a central enzyme in guanine nucleotide metabolism pathways, catalyzing the phosphorylation of (d)GMP to (d)GDP. The biochemistry, genetics, and regulation of Gmks in animals and microorganisms is well documented. However, little is known about enzymatic and signaling role of Gmk in higher plants. The rice virescent 2 (v2) mutant is altered in chloroplast differentiation and develops chloroplast-deficient leaves. Previously we isolated V2 gene by positional cloning and revealed that V2 gene (designated as mGmk) encodes a mitochondria-localized Gmk. While there are many reports of cytosolic Gmk in eukaryotes, much less is known of mGmk. Our data indicate that the mGmk is essential for chloroplast development. Rice has another Gmk gene (OGK1) encoding cytosolic Gmk. Moreover, Arabidopsis also has two types of enzymatically active Gmks. Through the comparison of these two Gmk genes, the functional significance of mGmk in mitochondria will be discussed.
