Abstract：

A newly identified PPRproteinCNS1regulates5 '-terminal integrity of ccmF(N) transcripts and affects the function ofmitochondrialcomplexIIIandseeddevelopment.

Mitochondrialfunction relies on theassemblyof electron transport chain complexes, which requires coordination between proteins encoded by the mitochondrion and those of the nucleus. Here, we cloned amaize(Zea mays) cytochrome c maturation F-N stabilizer1 (CNS1) and found it encodes apentatricopeptiderepeat(PPR)protein. Members of the PPR family are widely distributed in plants and are associated with RNA metabolism in organelles. P-type PPR proteins play essential roles in stabilizing the 3 '-end of RNA in mitochondria; whether a similar process exists for stabilizing the 5 '-terminus ofmitochondrialRNA remains unclear. The kernels ofcns1exhibited arrested embryo and endospermdevelopment, whereas neither conventional splicing deficiency nor RNA editing difference inmitochondrialgenes was observed. Instead, most of the ccmF(N) transcripts isolated fromcns1mutant plants were 5 '-truncated and therefore lacked the start codon. Biochemical and molecular data demonstrated thatCNS1is a P-type PPRproteinencoded by nuclear DNA and that it localizes to the mitochondrion. Also, one binding site ofCNS1located upstream of the start codon in the ccmF(N) transcript. Moreover, abnormalmitochondrialmorphology and dramatic upregulation of alternative oxidase genes were observed in the mutant. Together, these results indicate thatCNS1is essential for reaching a suitable level of intact ccmF(N) transcripts through binding to the 5 '-UTR of the RNAs and maintaining 5 '-integrity, which is crucial for sustainingmitochondrialcomplexIIIfunction to ensuremitochondrialbiogenesis andseeddevelopmentinmaize.

Keywords：CYTOCHROME-C BIOGENESIS；PPRPROTEIN；ABC TRANSPOR；TERMESSENGER-RNA；INTRON 1；ENCODES；DOMAIN；STABILIZES；GENES；TRANSCRIPTS