Group-II introns are self-splicing mobile genetic elements consisting of catalytic intron-RNA and its related intron-encoded splicing maturase protein cofactor. Group-II sequences are particularly plentiful within the mitochondria of land plants, where they reside within many critical gene loci. During evolution, the plant organellar introns have degenerated, such as they lack regions that are are required for splicing, and also lost their evolutionary related maturase proteins. Instead, for their splicing the organellar introns in plants rely on different host-acting protein cofactors, which may also provide a means to link cellular signals with respiratory functions. The nuclear genome of Arabidopsis thaliana encodes four maturase-related factors. Previously, we showed that three of the maturases, nMAT1, nMAT2 and nMAT4, function in the excision of different group-II introns in Arabidopsis mitochondria. The function of nMAT3 (encoded by the At5g04050 gene locus) was found to be essential during early embryogenesis. Using a modified embryo-rescue method, we show that nMAT3-knockout plants are strongly affected in the splicing of nad1 introns 1, 3 and 4 in Arabidopsis mitochondria, resulting in complex-I biogenesis defects and altered respiratory activities. Functional complementation of nMAT3 restored the organellar defects and embryo-arrested phenotypes associated with the nmat3 mutant line. Notably, nMAT3 and nMA4 were found to act on the same RNA targets but have no redundant functions in the splicing of nad1 transcripts. The two maturases, nMAT3 and nMAT4 are likely to cooperate together in the maturation of nad1 pre-RNAs. Our results provide important insights into the roles of maturases in mitochondria gene expression and the biogenesis of the respiratory system during early plant life.
Bibliographical noteFunding Information:
We thank Dr Michal Zmudjak for her help with establishing homozygous plants and Nadav Biran‐Ostersetzer for his help with figure preparation. We also wish to thank Dr Etienne Meyer (Martin Luther University of Halle‐Wittenberg) and Eduardo Zabaleta (Universidad Nacional de Mar del Plata) for providing us with anti‐NAD1 and CA2 antibodies, respectively. This work was supported by grants to OOB from the Israeli Science Foundation (ISF‐1834/20) and the Israel China Research Grant Program (NSFC‐ISF‐3254/20). nmat3‐1
We thank Dr Michal Zmudjak for her help with establishing homozygous nmat3-1 plants and Nadav Biran-Ostersetzer for his help with figure preparation. We also wish to thank Dr Etienne Meyer (Martin Luther University of Halle-Wittenberg) and Eduardo Zabaleta (Universidad Nacional de Mar del Plata) for providing us with anti-NAD1 and CA2 antibodies, respectively. This work was supported by grants to OOB from the Israeli Science Foundation (ISF-1834/20) and the Israel China Research Grant Program (NSFC-ISF-3254/20).
© 2021 Society for Experimental Biology and John Wiley & Sons Ltd
- Arabidopsis thaliana
- group-II intron