Deletion of a DnaK protein gene causes seedling green-revertible albino by retarding chloroplast development in rice

Green-revertible albino mutants are important sources for studying chloroplast structure, chloroplast development, chlorophyll biosynthesis, and plant photosynthesis. In the present study, we characterized a green-revertible albino mutant gra(k), which was obtained from the tissue-cultured rice Kitaake. The mutant gra(k) exhibited albino on its first three leaves. The leaf color started to turn green at the four-leaf stage. The chlorophyll contents were deeply reduced at the seedling stage, and the chloroplast development was delayed in gra(k). The green-revertible albino (gra) phenotype of the mutant gra(k) was temperature dependent. The main agronomic traits, including plant height, tilling number per plant, seed setting rate, and thousand-grain weight, slightly decreased in gra(k) comparing to those in the wild-type Kitaake. Genetic analysis showed that the gra phenotype was controlled by a single recessive nucleic gene. By using 5,168 recessive F2 individuals derived from the cross of gra(k) × Jodan, the locus of the gene Gra(k) was delimited in a DNA region of 200 kb between the makers B-31 and P11 on chromosome 5. Sequencing analysis indicated that the three functionally annotated genes, LOC_Os05g23700, LOC_Os05g23720, and LOC_Os05g23740, were all deleted in the 200 kb region in the mutant gra(k). Transgenic test revealed that the gra(k) plants over-expressing LOC_Os05g23740CDS were restored to normal green as the wild-type Kitaake. Our results proved that the deletion of the DnaK protein gene LOC_Os05g23740 (encoding the chaperon protein OsHsp70CP1) led to the gra phenotype in the mutant gra(k)