Importance of the rice TCD9 encoding α subunit of chaperonin protein 60 (Cpn60α) for the chloroplast development during the early leaf stage

The chloroplast development governs plant growth and metabolism. This study characterized a novel rice thermo-sensitive chloroplast development 9 (tcd9) mutant, which exhibited the albino phenotype before the 3-leaf stage grown below 24 degrees C whereas displayed normal green at over 28 degrees C or even at 20 degrees C after 5-leaf stage. The obvious decrease in Chl levels, abnormal chloroplasts with few thylakoid lamella and abnormal thylakoids were observed for the albino mutant seedlings at low temperature, but the mutant was apparently normal green at high temperature, suggesting the thermo-sensitivity of albino phenotype. Genetic analysis showed that the albino phenotype was controlled by a single recessive nuclear gene (tcd9). The map-based cloning and molecular complementation tests revealed that the mutation of TCD9 encoding alpha subunit of Cpn60 protein (Cpn60 alpha), localized in chloroplasts, was responsible for albino phenotype. In addition, TCD9 exhibited the high expression in all tested tissues, especially in young leaves. The transcriptional analysis indicated that all expression levels of the studied genes related to chloroplast development in tcd9 mutant were seriously affected in the albino seedlings at 20 degrees C, whereas some of them recovered into normal levels in green-seedlings at 32 degrees C. Our observations suggest that the nuclear-encoded Cpn60 alpha protein TCD9 plays a crucial role in chloroplast development at early leaf stage of rice. (C) 2013 Elsevier Ireland Ltd. All rights reserved.