A Methyltransferase, PTAC14, Involved In Chloroplast Development In Arabidopsis

pTAC14is one of the essential ingredients in chloroplast-encoded RNA polymerasecomplex, its T-DNA insertion mutants result to albino phenotype and seedling lethal.pTAC14interacts with pTAC12to regulate the expression of chloroplast genes.However, its biological function is unclear. This paper studied the pTAC14function.pTAC14possess SET domain and Rubis-binding domain. Bioinformatic analysisshowed that pTAC14protein has a number of conserved amino acid motif in thetypical SET lysine methyltransferase enzyme protein. Site mutagenesis and transgeniccomplementation analysis found that G103, N286, Y324amino acid residues isrequired to function of pTAC14protein. Pull down experiments in vitro showedthat,pTAC14can combine with Rubisco large subunit(rbcL). Methylation in vitroincubation experiments and Western blot experiments showed rbcL can be methylatedby pTAC14. These results indicate that pTAC14can act as methyltransferase enzymeto methylate rbcL. In addition, this paper also analyzed the accumulation of the coresubunit rpoA and PEP member pTAC12in the essential component of PEP deletionmutants, the results found that the accumulation of rpoA presented a downward trendin ptac7, ptac10, ptac14, trxZ and atpG albino mutants, and almost similar to theamount of rpoA in1/4wild-type. The same amount of accumulation of pTAC12inptac7and trxZ mutants, have showed serious decline, the expression of pTAC12inptac10and atpG T-DNA mutants were same as it in1/4wild type, and slightlydecreased in ptac14T-DNA mutant. We divided into six segments according pTAC14structural feature and constructed on pGBKT7vector, there hardly exist interactionbetween these six segments and pTAC12by yeast two-hybrid experiments. accordingto the results of this study, we guess the C-terminal adjacent domain in SETdomain-containing protein is a key part to complete the function of methyltransferase.In summary, these results indicate that pTAC14, as a member of TAC complexes, itsmethyltransferase activity play a of important role to chloroplast development.