Identification And Functions Of Chloroplast-Targeted J-protein Mutants In Arabidopsis

J-protein is a kind of protein which contains J-domain. Some J-proteins act as molecula chaperone. Genome sequence analysis showed that there are more than 120 J-Protein genes in Arabidopsis thaliana. Bioinformatics analysis showed that J-proteins distribute in a variety of cell organelles. AtJ8 is one of chloroplast-targeted J-proteins in Arabidopsis. The functions of AtJ8 gene in plant growth, development and environmental stress have not been reported so far. With AtJ8 T-DNA gene insertion mutants as the material, we compared phenotypic differences between AtJ8 mutants and wild-type in growth, development and environmental stress, in order to investigate the possible functions ofAtJ8 in plant life activities.T-DNA insertion homozygous mutants of AtJ8 gene were identified by PCR method. The transcript of AtJ8 gene in atj8-1 mutant was examined by RT-PCR. The result showed that atj8-1 mutant lacks full-length transcript, suggesting that AtJ8 gene is knocked-out because of the insertion of T-DNA. Further experiment showed that atj8-1 mutant has a single copy of T-DNA insertion.Under normal growth condition, phenotypes of atj8-1 mutant in the growth and development were observed and analyzed. The results indicated that atj8-1 mutant had much higher germination rate than wild type in the early stage of germination. After the 4th day, germination rate of atj8-1 and wild type reached similar level. The result suggested that AtJ8 gene possibly participated in the regulation of seeds germination. The roots of atj8-1 mutant were longer than those of wild type. In hypocotyl elongation, there was no significant difference between the mutant and the wild type.Resistance of plant to several environmental stresses was compared and analyzed in wild-type and atj8-1 mutant. Under cold, freeze or heat stress, there were no significant differences in viability of the seedling between atj8-1 mutant and wild type, indicating that the AtJ8 gene does not involve in the regulation process of adaptation of cold, freeze and heat stresses. Under salt or drought stress, the germination rate of atj8-1 mutant was higher than that of wild type, but the growth of roots had little difference between atj8-1 mutant and wild type. Further, we tested the effects of exogenous ABA on wild-type and atj8-1 mutant. The results showed that atj8-1 mutant seedlings were less sensitive to ABA than wild type in seed germination and the emergence of green cotyledon. However, atj8-1 mutant seedlings were ultra-sensitive to ABA in root growth. The results above suggest that AtJ8 gene may be involved in the regulation of osmotic stress, and this regulation is likely to depend on ABA.Real-time quantitative detection showed that, AtJ8 gene had the highest expression in the root, the second highest in the stem, and the third in seed pod, while it had the least expression in leaves and flower.Moreover, we identified other three T-DNA insertion mutants of J-protein family (AtJ11, AtJ17, AtJ120), and carried out a preliminary research to their functions in plant growth, development and environmental stress. No significant phenotypic differences were found between atj8-1 mutant and wild type.