A cytonuclear incompatibility causes anther sterility in Mimulus hybrids

Area of Science:

• Evolutionary Biology
• Genetics
• Plant Science

Background:

• Multilocus interactions, including Dobzhansky-Muller incompatibilities, are key drivers of hybrid inviability and sterility.
• Cytonuclear incompatibilities, arising from conflicts between cytoplasmic and nuclear genomes, are hypothesized to be early contributors to reproductive isolation.

Purpose of the Study:

• To investigate cytoplasm-dependent anther sterility in hybrids between Mimulus guttatus and Mimulus nasutus.
• To genetically map the nuclear locus responsible for this sterility and explore its relationship with other phenotypic traits.

Main Methods:

• Hybridization of Mimulus guttatus and Mimulus nasutus to create F1, F2, and backcross generations.
• Phenotypic analysis of anther morphology and flower size across different hybrid generations.
• Quantitative trait locus (QTL) mapping to identify the genetic basis of anther sterility and corolla width.

Main Results:

• A novel pollenless anther phenotype was observed in F2 hybrids with M. guttatus cytoplasm (F2G), indicating cytoplasm-dependent sterility.
• The anther sterility segregated as a single-locus recessive trait, mapped to LG7, and was named restorer-of-male-fertility (RMF).
• A major QTL for reduced corolla width co-localized with the RMF locus, suggesting pleiotropic effects.

Conclusions:

• The observed anther sterility likely results from a cryptic cytoplasmic male sterility (CMS) and restorer system within M. guttatus.
• The genetic mapping of RMF provides a foundation for studying the molecular basis and fitness consequences of CMS in plants.
• Cryptic CMS may play a significant, often overlooked, role in plant hybrid incompatibilities and interspecific introgression.