Cost of Having the Largest Mitochondrial Genome: Evolutionary Mechanism of Plant Mitochondrial Genome

Table 1

Unique ORFs that are fused with genuine mitochondrial genes.

Name of gene	Position of fused unique ORF^1	Detection of fused polypeptide	Detection of cleaved core region^2	Detection of cleaved extension^3	Note	References
Carrot atp8	C(57)	Yes	Yes^4	No		[84]
Carrot cox1	C(224, 284)	No	Yes	ND		[85]
Maize rps2A	C(330)	Yes	Yes	Yes		[86]
Sugar beet Gnad9-1	C(14)	Yes	No	ND^5	Complex I exhibits normal activity.	[71]
Sorghum cox1	C(101)	Yes	No	ND^5	Presumably associated with CMS.	[87]
Petunia atp6	N(145)	No^6	Yes	ND^5		[88]
Radish Ogura atp6	N(174)	No^6	Yes	ND^5		[89]
Sugar beet atp6	N(387)	No^6	Yes	Yes	Cleaved extension forms oligomer. Presumably associated with CMS.	[83]
Sugar beet ccmC	N(277)	Yes	Yes	No		[90]

¹C: carboxyl terminal; N: amino terminal; numbers in parenthesis indicate the amino acid residues encoded by the fused ORF.
²Polypeptides corresponding to the genuine mitochondrial gene.
³Polypeptides corresponding to the unique ORF.
⁴The extension may not be removed completely.
⁵ND: not determined.
⁶Polypeptides containing both the N-terminal extension and the core region of ATP6 have not been detected in any plant, perhaps due to rapid processing, or for unknown reasons (see references listed in the table).