Location: Tropical Crops and Germplasm ResearchTitle: Restorer-of-fertility mutations recovered in transposon-active lines of S male-sterile maize Author
|Gabay-laughnan, Susan - University Of Illinois|
|Settles, Mark - University Of Florida|
|Hannah, Curtis - University Of Florida|
|Porch, Timothy - Tim|
|Becraft, Philip - Iowa State University|
|Mccarty, Donald - University Of Florida|
|Koch, Karen - University Of Florida|
|Zhao, Liming - Florida Medical Entomology Laboratory|
|Kamps, Terry - New Jersey City University|
|Chamusco, Karen - University Of Florida|
|Chase, Christine - University Of Florida|
Submitted to: G3, Genes/Genomes/Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2017
Publication Date: 1/1/2018
Citation: Gabay-Laughnan, S., Settles, M., Hannah, C., Porch, T.G., Becraft, P., Mccarty, D., Koch, K.E., Zhao, L., Kamps, T., Chamusco, K., Chase, C. 2018. Restorer-of-fertility mutations recovered in transposon-active lines of S male-sterile maize. G3, Genes/Genomes/Genetics. 8:291-302. https://doi.org/10.1534/g3.117.300304.
DOI: https://doi.org/10.1534/g3.117.300304 Interpretive Summary: In the plant cell, mitochondria execute key pathways of central metabolism and serve as cellular sensing and signaling entities, functions that depend upon interactions between genes in the mitochondria and genes in the nucleus of the cell. This interaction is exemplified in a reproductive sterility system in corn, termed cytoplasmic male type S (CMS-S). In this system, a novel DNA sequence in the mitochondria is associated with the visible collapse of the pollen, but mutations in the nucleus, restorer-of-fertility (restorer) mutations, rescue pollen function, resulting in normal pollen. Reproductive fertility in corn plays a key role in the production of hybrids, and thus in yield and productivity of the crop. To better understand the roles and interactions of nucleus and mitochondria in reproduction, we screened populations of corn where active jumping genes, or transposons, cause mutations in genes throughout the corn genome, including Activator-Dissociation (Ac-Ds), Enhancer/Suppressor-mutator (En/Spm) and Mutator (Mu) transposon-active CMS-S stocks. These stocks were used to identify new genes, detected as mutants, which rescue pollen function. We found that the frequency of these pollen function restorer mutants increased in stocks with active transposons compared to stocks that had inactive transposons. While most mutants recovered from the Ac-Ds and En/Spm stocks were unstable, ten independent restorer mutations recovered from CMS-S Mu transposon stocks were stable. Eight mutants were evaluated with a seed-lethal allelism test to identify independent genes controlling the pollen restorer trait; seven new genes and two additional mutants in the rfl2-1 gene were found. Immunoblotting studies of pollen proteins from mutants demonstrated different nuclear versus mitochondria-encoded protein synthesis as compared to the normal pollen, thus showing metabolic plasticity in maize pollen. This and future studies of these mutants are providing new insights into mitochondrial functions critical to pollen and seed development.
Technical Abstract: Mitochondria execute key pathways of central metabolism and serve as cellular sensing and signaling entities - functions that depend upon interactions between mitochondrial and nuclear genetic systems. This is exemplified in cytoplasmic male sterility type S (CMS-S) of Zea mays, where novel mitochondrial open reading frames are associated with a pollen collapse phenotype, but nuclear restorer-of-fertility (restorer) mutations rescue pollen function. To better understand these genetic interactions, we screened Activator-Dissociation (Ac-Ds), Enhancer/Suppressor-mutator (En/Spm) and Mutator (Mu) transposon-active CMS-S stocks to recover new restorer mutants. The frequency of restorer mutations increased in transposon-active stocks compared to transposon-inactive stocks, but most mutants recovered from Ac-Ds and En/Spm stocks were unstable, reverting upon backcrossing to CMS-S inbred lines. Ten independent restorer mutations recovered from CMS-S Mu transposon stocks were, however, stable upon back crossing. Many restorer mutations condition seed-lethal phenotypes that provide a convenient test for allelism. Eight such mutants recovered in this study included one pair of allelic mutations that were also allelic to the previously described rfl2-1 mutant. Immunoblotting studies of pollen mitochondrial proteins demonstrated increased nuclear-encoded alternative oxidase relative to mitochondria-encoded cytochrome oxidase and decreased mitochondria-encoded ATP synthase subunit 1 compared to nuclear-encoded ATP synthase subunit 2 in restored S-cytoplasm pollen as compared to normal-cytoplasm, non-mutant pollen. Some restorer mutants were associated with depletion of additional mitochondria-encoded respiratory proteins. CMS-S restorer mutants thus revealed a metabolic plasticity in maize pollen, and further study of these mutants will provide new insights into mitochondrial functions critical to pollen and seed development.