Convergent Evolution Without Adaptation? Recurrent Switches of Alternative Pathways for an Essential Mitochondrial Process in Plants

This seminar is co-sponsored by the Huck Institutes of the Life Sciences' Plant Biology Program and the Plant Institute.

Abstract:
Cytochrome c maturation (CCM) is an essential mitochondrial process that requires heme attachment to cytochromes c and c1 and proceeds by distinct biogenesis pathways termed system I and system III. The mosaic distribution of CCM systems I and III among Archaeplastida species raises questions about the underlying genetic mechanisms and evolutionary forces that promote convergent evolution. Using comparative genomic and mitogenomic analysis, we show that the recurrent loss of system I is compensated by the parallel gain of a system III holocytochrome c synthase (HCCS) in at least 11 diverse archaeplastid lineages. HCCS homologs from the fern Ceratopteris richardii and the model green alga Chlamydomonas reinhardtii are sufficient to rescue yeast HCCS deletion lines grown under respiratory conditions. C. reinhardtii HCCS mutants created by CRISPR-Cas9 show slowed growth, altered TCA metabolism, and impaired respiration with low activity of the cytochrome c-dependent respiratory chain, likely the result of deficient CCM that leads to the malfunction of mitochondrial complex III and/or complex IV. Collectively, these results demonstrate that plant and algal HCCS homologs are functional system III components for mitochondrial CCM in the absence of system I. Moreover, they elucidate the evolutionary trajectory and functional divergence of CCM pathways among Archaeplastida and provide new insight into the causes, mechanisms, and consequences of repeated cooption of an entire biological pathway via convergent evolution.

About the Speaker:
Jeff Mower works in the Center for Plant Science Innovation and the Department of Agronomy and Horticulture at the University of Nebraska-Lincoln. He has >60 publications on topics related to the evolutionary and functional genomics of plants (https://scholar.google.com/citations?hl=en&user=houXa9kAAAAJ). The CCM project is funded by NSF.

Contact

Sally Mackenzie
sam795@psu.edu