Experimental evolution of an alternating uni- and multicellular life cycle in Chlamydomonas reinhardtii

The distribution of fitness effects (DFE) for new mutations is fundamental for many aspects of population and quantitative genetics. In this study, we have inferred the DFE in the single-celled alga Chlamydomonas reinhardtii by estimating changes in the frequencies of 254 spontaneous mutations under experimental evolution and equating the frequency changes of linked mutations with their selection coefficients. We generated seven populations of recombinant haplotypes by crossing seven independently derived mutation accumulation lines carrying an average of 36 mutations in the homozygous state to a mutation-free strain of the same genotype. We then allowed the populations to evolve under natural selection in the laboratory by serial transfer in liquid culture. We observed substantial and repeatable changes in the frequencies of many groups of linked mutations, and, surprisingly, as many mutations were observed to increase as decrease in frequency. We developed a Bayesian Monte Carlo Markov Chain method to infer the DFE. This computes the likelihood of the observed distribution of changes of frequency, and obtains the posterior distribution of the selective effects of individual mutations, while assuming a two-sided gamma distribution of effects. We infer that the DFE is a highly leptokurtic distribution, and that approximately equal proportions of mutations have positive and negative effects on fitness. This result is consistent with what we have observed in previous work on a different C. reinhardtii strain, and suggests that a high fraction of new spontaneously arisen mutations are advantageous in a simple laboratory environment.

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Abscisic acid confers salinity tolerance in Chlamydomonas reinhardtii at different stages of its life cycle

10.22541/au.159231497.73328000 ◽

2020 ◽

Author(s):

Said Abu Ghosh ◽

Zvy Dubinsky ◽

David Iluz

Keyword(s):

Abscisic Acid ◽

Life Cycle ◽

Chlamydomonas Reinhardtii ◽

Salinity Tolerance

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Genetic Structure of the Mating-Type Locus of Chlamydomonas reinhardtii

Genetics ◽

10.1093/genetics/160.1.181 ◽

2002 ◽

Vol 160 (1) ◽

pp. 181-200

Author(s):

Patrick J Ferris ◽

E Virginia Armbrust ◽

Ursula W Goodenough

Keyword(s):

Life Cycle ◽

Chlamydomonas Reinhardtii ◽

Mating Type ◽

Housekeeping Genes ◽

Pyruvate Dehydrogenase Kinase ◽

Northern Analysis ◽

Uniparental Inheritance ◽

Coding Region ◽

Type Locus ◽

Mutational Change

Abstract Portions of the cloned mating-type (MT) loci (mt+ and mt−) of Chlamydomonas reinhardtii, defined as the ~1-Mb domains of linkage group VI that are under recombinational suppression, were subjected to Northern analysis to elucidate their coding capacity. The four central rearranged segments of the loci were found to contain both housekeeping genes (expressed during several life-cycle stages) and mating-related genes, while the sequences unique to mt+ or mt− carried genes expressed only in the gametic or zygotic phases of the life cycle. One of these genes, Mtd1, is a candidate participant in gametic cell fusion; two others, Mta1 and Ezy2, are candidate participants in the uniparental inheritance of chloroplast DNA. The identified housekeeping genes include Pdk, encoding pyruvate dehydrogenase kinase, and GdcH, encoding glycine decarboxylase complex subunit H. Unusual genetic configurations include three genes whose sequences overlap, one gene that has inserted into the coding region of another, several genes that have been inactivated by rearrangements in the region, and genes that have undergone tandem duplication. This report extends our original conclusion that the MT locus has incurred high levels of mutational change.

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