Expression of ubiquitin genes in Chlamydomonas reinhardtii: involvement in stress response and cell cycle

Abstract

Abstract. Applying different stresses (heat shock, photoinhibition, and chilling) to the unicellular green alga Chlamydomonas reinhardtii led to a characteristic transcription pattern of mRNAs encoding ubiquitin extension proteins [0.7-kb transcript(s)] as well as polyubiquitin (2.3-kb transcript). Heat shock resulted in an increase in the amount of polyubiquitin mRNA (up to tenfold compared with control cells). Chilling in the light led to a sevenfold increase in the amount of 2.3-kb transcript and to a twofold increase in the amount of 0.7-kb mRNA(s), whereas a less pronounced effect on the level of the polyubiquitin transcript was observed after applying either chilling in darkness or photoinhibition. The latter stress, however, led to a dramatic decrease in mRNAs encoding ubiquitin extension proteins (down to 23% of control cells). Experiments performed with a temperature-sensitive cell-cycle mutant of C. reinhardtii showed that the 2.3-kb polyubiquitin mRNA was no longer transcribed when cells were shifted to a non-permissive temperature, and thus were blocked in their vegetative cell cycle. This leads to the assumption that the expression of the corresponding gene is necessary for completion of the C. reinhar&ii vegetative cell cycle.

Comparative transcriptomics analysis reveals difference of key gene expression between banana and plantain in response to cold stress

“…UBQ (poly-ubiquitin gene) is involved in protein hydrolysis in the ubiquitin-proteasome pathway. In order to compensate cells for ubiquitin molecules in signal transmission, expression of poly-ubiquitin gene is increased in response to stress [ 52 ]. Given the increased expression of UBQ in response to cold treatment, we suspect that UBQ might be involved in stress response in plantain.…”

The ultrastructure of chilling stress

“…In other words, are the observed symptoms strictly the result of a direct effect of temperature, or are they caused indirectly by programmed genetic mechanisms that are activated by the initial environmental insult? Chilling stress induces changes in gene expression ( Guy 1990) that may be related to protective pathways ( Sabehat, Lurie & Weiss 1998) or to degradative pathways ( von Kampen, Nielander & Wettern 1995). In this regard, it may be prudent to ask to what extent the ultrastructural changes occurring during chilling injury may be related to similar symptoms seen in mammalian cells during apoptosis.…”

The ubiquitin-proteasome pathway protects Chlamydomonas reinhardtii against selenite toxicity, but is impaired as reactive oxygen species accumulate

“…In the green alga Chlamydomonas, the UPP is known to have a role in flagella development ( Huang et al 2009 ) and the degradation of sulfate transporters ( Pootakham et al 2010 ), but its function in mitigating abiotic stress has not been fully investigated and only indirectly implicated. For example, chilling and heat stress increased the transcript abundance of ubiquitin in Chlamydomonas ( von Kampen et al 1995 ). Methyl viologen treatment generates superoxide accompanied with the accumulation of ubiquitinated proteins in Chlamydomonas ( Shimogawara and Muto 1991 ); this likely suggests that the varied types of abiotic stress that induce superoxide would likewise increase the level of ubiquitinated proteins in Chlamydomonas .…”