#CGMS

Plant Breeding 2

R-line in CGMS contains:

R-line known as restorer line harbors dominant restorer of fertility genes Rf encoding pentatricopeptide repeat proteins targeted to mitochondria where they bind and cleave aberrant ORF transcripts such as orf79 associated with WA cytoplasm in rice, restoring normal oxidative phosphorylation and ATP supply for anther development. Genotype RfRf, cytoplasm may be either S or N but crucial nuclear contribution dominates. Cross between A-line rfrf and R-line RfRf produces F1 heterozygote Rfrf where restorer protein suppresses sterility causing ORF, enabling normal pollen development and full male

Ref: Huang et al Nature 2015 Rf cloning rice; Bentolila et al PPR restorer mechanism; PubMed Restorer genetics review.

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Plant Breeding 2

B-line in CGMS is used to:

B-line or maintainer line defined as fertile counterpart isogenic to A-line for nuclear genes but carrying normal fertile cytoplasm N and homozygous non-restorer alleles rfrf. Function maintains male sterile A-line because when A-line cytoplasm S mother crossed with pollen from B-line, offspring inherits S cytoplasm from maternal parent causing male sterility while nuclear genome remains rfrf identical to both parents. B-line itself self-fertile due to N cytoplasm compensating, producing sufficient seeds for propagation. Without B-line, A-line cannot be multiplied sexually because selfing yiel

Ref: Singh BD Maintainer line role; Acquaah Principles B-line multiplication; ICAR Hybrid seed Handbook.

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Plant Breeding 2

In CGMS, A-line is:

In CGMS three-line scheme A-line designated as cytoplasmic male sterile female parent carrying sterile cytoplasm S derived from wild abortive source and non-restorer genotype rfrf in nuclear background, so phenotype fully male sterile with whitish anthers containing aborted pollen but female fertility normal. Because cytoplasm maternally inherited, progeny from any cross where A-line used as female inherits S cytoplasm and remains sterile unless restorer allele introduced from male parent. To multiply A-line, cross made with maintainer B-line sharing identical nuclear genome but normal fertile

Ref: Singh BD CGMS A-line definition; Rice Knowledge Portal Three line system; Acquaah Hybrid breeding A-line.

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Plant Breeding 2

CGMS involves interaction between:

Cytoplasmic-genic male sterility arises from antagonistic interaction between mitochondrial genome carrying sterility causing chimeric open reading frames and nuclear genome harboring restorer of fertility Rf genes. Mitochondrial ORFs such as orf79 in rice WA cytoplasm, orf138 in Brassica Ogu cytoplasm resulting from rearrangement generate cytotoxic peptides disrupting mitochondrial electron transport complex assembly reducing ATP supply critical for high energy demand of tapetal cells during microsporogenesis. Cytoplasm S with ORF confers sterility when nuclear background homozygous for non-r

Ref: Hanson MR Bentolila Annu Rev Genetics CMS molecular basis; Fujii PPR restorer mechanism Plant Cell; Singh BD CGMS interaction.

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