Abstract
Arabidopsis crr4 mutants were identified by their lack in NDH activity. CRR4 encodes a putative chloroplast-targeting protein with PPR motifs. The RNA editing that creates an ndhD initiation codon was specifically impaired in crr4. In the structure, CRR4 is similar to CRR2 involve in a specific RNA cutting in the chloroplast. We hypothesize that PPR proteins recognize the target RNA and interact with other general factors involved in RNA maturation.
In Arabidopsis, approximately half of ndhD initiation codon was edited in leaves, with less efficiency in etiolated seedlings and no RNA was edited in roots. To study the possible relationship between the CRR4 expression level and the editing efficiency, CRR4 was overexpressed in crr4. Despite the complementation of the editing, the efficiency was not more that the wild-type level. No RNA editing was detected in roots. Unknown factor other than PPR protein may limit the efficiency of RNA editing.
