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The genetic background between strains of a single species and within a single strain lineage can significantly impact the expression of biological traits. This genetic variation may also reshape epigenetic mechanisms of cell identity and environmental responses that are controlled by interconnected transcriptional networks and chromatin-modifying enzymes. Histone deacetylases, including sirtuins, are critical regulators of chromatin state and have been directly implicated in governing the phenotypic transition between the ‘sterile’ white state and the mating-competent opaque state inCandida albicans,a common fungal commensal and pathogen of humans. Here, we found that a previously ambiguous role for the sirtuinSIR2inC. albicansphenotypic switching is likely linked to the genetic background of mutant strains produced in the RM lineage of SC5314.SIR2mutants in a specific lineage of BWP17 displayed increased frequencies of switching to the opaque state compared to the wild-type. Loss ofSIR2in other SC5314-derived backgrounds, including newly constructed BWP17sir2Δ/Δ mutants, failed to recapitulate the increased white–opaque switching frequencies observed in the original BWP17sir2Δ/Δ mutant background. Whole-genome sequencing revealed the presence of multiple imbalanced chromosomes and large loss of heterozygosity tracts that likely interact withSIR2to increase phenotypic switching in this BWP17sir2Δ/Δ mutant lineage. These genomic changes are not found in other SC5314-derivedsir2Δ/Δ mutants that do not display increased opaque cell formation. Thus, complex karyotypes can emerge during strain construction that modify mutant phenotypes and highlight the importance of validating strain background when interpreting phenotypes.
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Comparative Phenotyping of Two Commonly Used Chlamydomonas reinhardtii Background Strains: CC-1690 (21gr) and CC-5325 (The CLiP Mutant Library Background)
The unicellular green alga Chlamydomonas reinhardtii is an excellent model organism to investigate many essential cellular processes in photosynthetic eukaryotes. Two commonly used background strains of Chlamydomonas are CC-1690 and CC-5325. CC-1690, also called 21gr, has been used for the Chlamydomonas genome project and several transcriptome analyses. CC-5325 is the background strain for the Chlamydomonas Library Project (CLiP). Photosynthetic performance in CC-5325 has not been evaluated in comparison with CC-1690. Additionally, CC-5325 is often considered to be cell-wall deficient, although detailed analysis is missing. The circadian rhythms in CC-5325 are also unclear. To fill these knowledge gaps and facilitate the use of the CLiP mutant library for various screens, we performed phenotypic comparisons between CC-1690 and CC-5325. Our results showed that CC-5325 grew faster heterotrophically in dark and equally well in mixotrophic liquid medium as compared to CC-1690. CC-5325 had lower photosynthetic efficiency and was more heat-sensitive than CC-1690. Furthermore, CC-5325 had an intact cell wall which had comparable integrity to that in CC-1690 but appeared to have reduced thickness. Additionally, CC-5325 could perform phototaxis, but could not maintain a sustained circadian rhythm of phototaxis as CC1690 did. Finally, in comparison to CC-1690, CC-5325 had longer cilia in the medium with acetate but slower swimming speed in the medium without nitrogen and acetate. Our results will be useful for researchers in the Chlamydomonas community to choose suitable background strains for mutant analysis and employ the CLiP mutant library for genome-wide mutant screens under appropriate conditions, especially in the areas of photosynthesis, thermotolerance, cell wall, and circadian rhythms.
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- Award ID(s):
- 2018962
- PAR ID:
- 10487462
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Plants
- Volume:
- 11
- Issue:
- 5
- ISSN:
- 2223-7747
- Page Range / eLocation ID:
- 585
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/plants11050585
