Transcript processing internal to a mitochondrial open reading frame is correlated with fertility restoration in male‐sterile sorghum

Abstract

SummaryA chimeric mitochondrial DNA (mtDNA) configuration of the cytoplasmic male-sterile (cms) sorghum line ISl112C includes a 321 bp open reading frame designated orfl07, encoding a predicted polypeptide product of 11.85 kDa. The open reading frame, similar to several other genes associated with cms, consists of amino-terminal sequences derived from an obligate gene. Unlike other examples to date, however, the carboxy-terminal 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 orfl07 are 84% similar to atp9, and the carboxy-terminal 49 residues are 57% identical and 80% similar to the carboxy terminus of orf79. Transcripts of off107 are edited, with four C-to-U changes that alter amino acids. Sorghum lines partially or fully restored to fertility exhibit a high-efficiency internal-orfl07 transcript processing activity, precluding abundant wholelength transcripts, while male-sterile lines exhibit only a trace of the activity. Previous data on the abundance of a 12 kDa in organello-synthesized polypeptide in male-sterile versus male-fertile lines are correlated with differential o#107 transcript processing activity of these lines. Examinations of backcross and F 2 lines suggest a gametophytic mode of restoration, and indicate that enhanced transcript processing activity is necessary, but not sufficient, to restore full fertility. These novel observations indicate that mitochondrial open reading frames associated with cms

Cell type-specific loss of atp6 RNA editing in cytoplasmic male sterile Sorghum bicolor

“…All F2 plants exhibit normal atp6 RNA editing activity. This result can be explained by the gametophytic mode of fertility restoration in S. bicolor (9), wherein only gametes carrying requisite fertility restoration genes are viable. Thus, no sterile plants are expected in the F2 generation, and these fertile plants should be able to edit atp6 transcripts, if one assumes that pollen is not viable without atp6 RNA editing.…”

“…Moreover, the restoration of fertility in F1 and F2 lines (see ref. 9) correlates with an increase of RNA editing of atp6 transcripts. Analysis of F2 plants indicates the involvement of dominant genes, which resemble cms restorer genes.…”

“…A multipartite mt structure due to recombination events was first observed in Brassica campestris (6), and appears to be a general feature of higher plants (7). One of the consequences of recombinational activity in higher plant mitochondria is the generation of chimeric reading frames (crf), e.g., the crf pcf found in petunia (8), orf107 of Sorghum bicolor line IS1112C (9), and T-urf13 found in the T cytoplasm of Zea mays (10)(11)(12), which is generated from nonprotein-coding sequences only.…”

Interactions of Mitochondrial and Nuclear Genes That Affect Male Gametophyte Development

“…A chimeric gene termed orf107 predicts a protein carrying an N-terminal region related to the N terminus of ATP9 (Tang et al, 1996(Tang et al, , 1999. The atp9-homologous region of sorghum orf107 has 23 of 31 residues identical to those of atp9, followed by a region in which 28 of 51 codons predict amino acids identical to those of the CMS-associated rice orf79 (Figure 1).…”

Bioengineering of Male Sterility in Rice (Oryza sativa L.)

“…It is only expressed in the presence of the sterile cytoplasm. Several previous reports demonstrated the relationship of Rf gene and sterile cytoplasm (Tang et al 1996). CGMS can be restored by Rf genes associated with nuclear genes mostly encoding pentatricopeptide repeat (PPR) proteins (Hanson and Bentolila 2004).…”