Jan 11

Comparative plastid genomics of Cryptomonas species reveals fine-scale genomic responses to loss of photosynthesis.


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Comparative plastid genomics of Cryptomonas species reveals fine-scale genomic responses to loss of photosynthesis.

Genome Biol Evol. 2020 Jan 10;:

Authors: Tanifuji G, Kamikawa R, Moore CE, Mills T, Onodera NT, Kashiyama Y, Archibald JM, Inagaki Y, Hashimoto T

Abstract
Loss of photosynthesis is a recurring theme in eukaryotic evolution. In organisms that have lost the ability to photosynthesize, non-photosynthetic plastids are retained because they play essential roles in processes other than photosynthesis. The unicellular algal genus Cryptomonas contains both photosynthetic and non-photosynthetic members, the latter having lost the ability to photosynthesize on at least three separate occasions. To elucidate the evolutionary processes underlying the loss of photosynthesis, we sequenced the plastid genomes of two non-photosynthetic strains, Cryptomonas sp. CCAC1634B and SAG977-2f, as well as the genome of the phototroph C. curvata CCAP979/52. These three genome sequences were compared to the previously sequenced plastid genome of the non-photosynthetic species C. paramecium CCAP977/2a as well as photosynthetic members of the Cryptomonadales, including C. curvata FBCC300012D. Intraspecies comparison between the two C. curvata strains showed that while their genome structures are stable, the substitution rates of their genes are relatively high. Although most photosynthesis-associated genes, such as the psa and psb gene families, were found to have disappeared from the non-photosynthetic strains, at least ten pseudogenes are retained in SAG977-2f. While gene order is roughly shared among the plastid genomes of photosynthetic Cryptomonadales, genome rearrangements are seen more frequently in the smaller genomes of the non-photosynthetic strains. Intriguingly, the light-independent protochlorophyllide reductase comprising ChlB, L, and N is retained in non-photosynthetic SAG977-2f and CCAC1634B. On the other hand, whereas CCAP977/2a retains ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO)-related genes, including rbcL, rbcS, and cbbX, the plastid genomes of the other two non-photosynthetic strains have lost the RuBisCO protein-coding genes.

PMID: 31922581 [PubMed – as supplied by publisher]