Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, USA.
Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA.
G3 (Bethesda). 2024 Oct 7;14(10). doi: 10.1093/g3journal/jkae201.
The interaction of plant mitochondrial and nuclear genetic systems is exemplified by mitochondria-encoded cytoplasmic male sterility (CMS) under the control of nuclear restorer-of-fertility genes. The S type of CMS in maize is characterized by a pollen collapse phenotype and a unique paradigm for fertility restoration in which numerous nuclear restorer-of-fertility lethal mutations rescue pollen function but condition homozygous-lethal seed phenotypes. Two nonallelic restorer mutations recovered from Mutator transposon-active lines were investigated to determine the mechanisms of pollen fertility restoration and seed lethality. Mu Illumina sequencing of transposon-flanking regions identified insertion alleles of nuclear genes encoding mitochondrial ribosomal proteins RPL6 and RPL14 as candidate restorer-of-fertility lethal mutations. Both candidates were associated with lowered abundance of mitochondria-encoded proteins in developing maize pollen, and the rpl14 mutant candidate was confirmed by independent insertion alleles. While the restored pollen functioned despite reduced accumulation of mitochondrial respiratory proteins, normal-cytoplasm plants heterozygous for the mutant alleles showed a significant pollen transmission bias in favor of the nonmutant Rpl6 and Rpl14 alleles. CMS-S fertility restoration affords a unique forward genetic approach to investigate the mitochondrial requirements for, and contributions to, pollen and seed development.
植物线粒体和核遗传系统的相互作用体现在核育性恢复基因控制下的线粒体编码细胞质雄性不育（CMS）上。玉米中的 S 型 CMS 表现为花粉崩溃表型，以及一种独特的育性恢复范例，其中许多核育性恢复致死突变挽救了花粉功能，但条件是纯合致死种子表型。从 Mutator 转座子活性系中恢复的两个非等位恢复突变被研究以确定花粉育性恢复和种子致死的机制。Mu Illumina 转座子侧翼区测序鉴定了编码线粒体核糖体蛋白 RPL6 和 RPL14 的核基因的插入等位基因，作为候选育性恢复致死突变。这两个候选基因都与发育中的玉米花粉中线粒体编码蛋白的丰度降低有关，并且 rpl14 突变体候选基因被独立的插入等位基因证实。虽然恢复的花粉功能尽管线粒体呼吸蛋白积累减少，但突变等位基因杂合的正常细胞质植物在有利于非突变 Rpl6 和 Rpl14 等位基因的花粉传递中表现出显著的偏倚。CMS-S 育性恢复为研究线粒体对花粉和种子发育的要求和贡献提供了一种独特的正向遗传学方法。
