Abstract: Chlorophylls are essential for photosynthesis. Chlorophyll biosynthesis is catalyzed by a series of enzyme complexes, such as Mgprotoporphyrin IX methyltransferase. A yellow mutant of Arabidopsis was isolated using an enthylmethane sulfonate (EMS) mutagenesis strategy. Chlorophyll content dramatically reduced and grana stacking was absent in the mutant. Genetic analysis indicated that the mutant was controlled by a single recessive gene. Using mapbased cloning strategy, the gene responsible for the mutant phenotype was mapped to a region of 114 kb between the molecular markers F13M23 and T30C3 on chromosome 4, in which the CHLM gene encoding Mgprotoporphyrin IX methyltransferase was included. The mutant was proved to be an allelic mutant of CHLM gene by sequencing and allelism test and then was designated as chlm4. Gly59 of CHLM was replaced by Glu59 in chlm4, which indicated that Gly59 was essential for the function of Mgprotoporphyrin IX methyltransferase.

Key words: Arabidopsis thaliana