Hv. Tang et al., TRANSCRIPT PROCESSING INTERNAL TO A MITOCHONDRIAL OPEN READING FRAME IS CORRELATED WITH FERTILITY RESTORATION IN MALE-STERILE SORGHUM, Plant journal, 10(1), 1996, pp. 123-133
A chimeric mitochondrial DNA (mtDNA) configuration of the cytoplasmic
male-sterile (cms) sorghum line IS1112C includes a 321 bp open reading
frame designated orf107, encoding a predicted polypeptide product of
11.85 kDa. The open reading frame, similar to several other genes asso
ciated with cms, consists of amino-terminal sequences derived from an
obligate gene. Unlike other examples to date, however, the carboxy-ter
minal sequences are highly similar to the carboxy terminus of an open
reading frame implicated in cms of rice, orf79. The amino-terminal 31
residues of orf107 are 84% similar to atp9, and the carboxy-terminal 4
9 residues are 57% identical and 80% similar to the carboxy terminus o
f orf79. Transcripts of orf107 are edited, with four C-to-U changes th
at alter amino acids. Sorghum lines partially or fully restored to fer
tility exhibit a high-efficiency internal-orf107 transcript processing
activity, precluding abundant whole-length transcripts, while male-st
erile lines exhibit only a trace of the activity. Previous data on the
abundance of a 12 kDa in organello-synthesized polypeptide in male-st
erile versus male-fertile lines are correlated with differential orf10
7 transcript processing activity of these lines. Examinations of backc
ross and F-2 lines suggest a gametophytic mode of restoration, and ind
icate that enhanced transcript processing activity is necessary, but n
ot sufficient, to restore full fertility. These novel observations ind
icate that mitochondrial open reading frames associated with cms in di
fferent species can include highly similar motifs, and that fertility
restoration could involve a mechanism by which synthesis of a ems-asso
ciated gene product may be precluded through internal transcript cleav
age.