Abstract
RNA splicing is an essential post-transcriptional regulation in plant mitochondria and chloroplasts. As the mechanism of RNA splicing remains obscure, identification and functional elucidation of new splicing factors are necessary. Through a characterization of two maize mutants, we cloned Empty pericarp 24 (Emp24) and Empty pericarp 25 (Emp25). Both Emp24 and Emp25 encode mitochondrion-targeted P-type PPR proteins. EMP24 is required for the splicing of nad4 introns 1 and 3, which was reported (Ren Z. et al., 2019), and EMP25 functions in the splicing of nad5 introns 1, 2, and 3. Absence of either Nad4 or Nad5 proteins blocks the assembly of mitochondrial complex I, resulting in the formation of a sub-sized complex I of similar size in both mutants. Mass spectrometry identification revealed that the subcomplexes in both mutants lack an identical set of proteins of complex I. These results indicate that EMP24 and EMP25 function in the splicing of nad4 and nad5 introns, respectively, and are essential to maize kernel development. The identification of the subcomplexes provides genetic and molecular insights into the modular complex I assembly pathway in maize.
Highlights
Mitochondria are the main energy powerhouse of the cell, which perform oxidative phosphorylation through the electron transport chain (ETC) (Knoop, 2013)
Self-pollinated heterozygotes for emp24-2 segregated emp kernels in a recessive manner, and crosses between emp24-1 and emp24-2 produced emp kernels (Supplementary Figure S2A). These results confirmed that GRMZM2G464510, which has been identified as Emp602 encodes a P-type pentatricopeptide repeat (PPR) protein that is specific for the splicing of mitochondrial nad4 introns 1 and 3 (Ren Z. et al, 2019), is the causal gene for the emp24 phenotype
Empty pericarp 24 (Emp24) has been identified as Emp602 that encodes a mitochondrionlocalized P-type PPR protein, which functions in the splicing of nad4 introns 1 and 3 (Ren Z. et al, 2019)
Summary
Mitochondria are the main energy powerhouse of the cell, which perform oxidative phosphorylation through the electron transport chain (ETC) (Knoop, 2013). The cytochrome pathway of ETC is composed of four protein complexes, I, II, III, and IV. Complex I (NADH dehydrogenase) is the inception point of ETC, which functions to remove two electrons from NADH and transfers to ubiquinone (UQ). Complex II (succinate dehydrogenase) is a parallel electron transport pathway to complex I and delivers additional electrons to the quinone pool (Q). Complex III (cytochrome c reductase) transfers electrons from ubiquinol to cytochrome c, which is a water-soluble electron carrier. Complex IV (cytochrome c oxidase) removes electrons
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