Temperature-sensitive Arabidopsis mutant defective in 1-deoxy-D-xylulose 5-phosphate synthase within the plastid non-mevalonate pathway of isoprenoidbiosynthesis

The temperature-sensitive mutant of Arabidopsis, chs5, developed chlorotic leaves at restrictive temperatures (15 degrees C), but almost normal green leaves at permissive temperatures (22 degrees C). At the restrictive temper ature, the chs5 mutation blocked the accumulation of chlorophylls and carot enoids. A temperature-shift analysis revealed that the manifestation of the chlorotic phenotype occurred in young leaf tissues, but did not in mature leaf tissues. Genetic and sequence analysis demonstrated that the chs5 muta tion was caused by a single-base change in the coding region of a recently identified CLA1 gene. The CLA1 gene exhibited a high sequence similarity to the genes encoding I-deoxy-D-xylulose 5-phosphate synthase (DXS) localized to the non-mevalonate pathway, which was recently discovered in bacteria a nd higher plants. In addition, the application of 1-deoxy-D-xylulose, the f ree sugar of I-deoxy-D-xylulose 5-phosphate, rescues the defect in the chs5 mutant. These results indicated that the chlorotic phenotype of the chs5 m utant was caused by a defect in DXS activity and that DXS functions prefere ntially at an early stage of leaf cell development. A transiently expressed green fluorescent protein fused with the CLA1 transit peptide was localize d within the chloroplasts in the green cultured cells of tobacco, which sug gests that the putative localization of the non-mevalonate pathway is in pl astids.