Functional divergence of chloroplast Cpn60? subunits during Arabidopsis embryo development.

ABSTRACT: Chaperonins are a class of molecular chaperones that assist in the folding and assembly of a wide range of substrates. In plants, chloroplast chaperonins are composed of two different types of subunits, Cpn60? and Cpn60?, and duplication of Cpn60? and Cpn60? genes occurs in a high proportion of plants. However, the importance of multiple Cpn60? and Cpn60? genes in plants is poorly understood. In this study, we found that loss-of-function of CPNA2 (AtCpn60?2), a gene encoding the minor Cpn60? subunit in Arabidopsis thaliana, resulted in arrested embryo development at the globular stage, whereas the other AtCpn60? gene encoding the dominant Cpn60? subunit, CPNA1 (AtCpn60?1), mainly affected embryonic cotyledon development at the torpedo stage and thereafter. Further studies demonstrated that CPNA2 can form a functional chaperonin with CPNB2 (AtCpn60?2) and CPNB3 (AtCpn60?3), while the functional partners of CPNA1 are CPNB1 (AtCpn60?1) and CPNB2. We also revealed that the functional chaperonin containing CPNA2 could assist the folding of a specific substrate, KASI (?-ketoacyl-[acyl carrier protein] synthase I), and that the KASI protein level was remarkably reduced due to loss-of-function of CPNA2. Furthermore, the reduction in the KASI protein level was shown to be the possible cause for the arrest of cpna2 embryos. Our findings indicate that the two Cpn60? subunits in Arabidopsis play different roles during embryo development through forming distinct chaperonins with specific AtCpn60? to assist the folding of particular substrates, thus providing novel insights into functional divergence of Cpn60? subunits in plants.

SUBMITTER: Ke X 

PROVIDER: S-EPMC5636168 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature