A Musashi Splice Variant and Its Interaction Partners Influence Temperature Acclimation in Chlamydomonas

Abstract

ORCID ID: 0000-0003-3414-9850 (M.M.)Microalgae contribute significantly to carbon fixation on Earth. Global warming influences their physiology and growth rates. To understand algal short-term acclimation and adaptation to changes in ambient temperature, it is essential to identify and characterize the molecular components that sense small temperature changes as well as the downstream signaling networks and physiological responses. Here, we used the green biflagellate alga Chlamydomonas reinhardtii as a model system in which to study responses to temperature. We report that an RNA recognition motif (RRM)-containing RNA-binding protein, Musashi, occurs in 25 putative splice variants. These variants bear one, two, and three RRM domains or even lack RRM domains. The most abundant Musashi variant, 12, with a molecular mass of 60 kD, interacts with two clock-relevant members of RNA metabolism, the subunit C3 of the RNA-binding protein CHLAMY1 and the 5ʹ-3ʹ exoribonuclease XRN1. These proteins are able to integrate temperature information by up-or down-regulation of their protein levels in cells grown at low (18°C) or high (28°C) temperature. We further show that the 60-kD Musashi variants with three RRM domains can bind to (UG) 7 repeat-containing RNAs and are up-regulated in cells grown at a higher temperature during early night. Intriguingly, the 60-kD Musashi variant 12, as well as C3 and XRN1, confer thermal acclimation to C. reinhardtii, as shown with mutant lines. Our data suggest that these three proteins of the RNA metabolism machinery are key members of the thermal signaling network in C. reinhardtii.

A Musashi-Related Protein is Essential for Gametogenesis in Arabidopsis

“…One of the resultant clades (‘plants I’) comprises single Arabidopsis ( At1g17640 ) and moss ( Physcomitrella patens ) genes plus duplicated algal ( Chlamydomonas reinhardtii ) and monocot ( Oryza sativa, Sorghum bicolor ) genes. One of the Msi genes from C. reinhardtii (Cre12.g560300.t1.2) has previously been shown to play a role in thermal signalling but phylogenetic analyses in the same study did not identify the second (Cre07.g330300.t1.2) (Li et al, 2018). Although algal genes are not represented in the second clade (‘plants II’), multiple duplications are evident in each of the 5 plant genomes.…”

Cold Adaptation Mechanisms of a Snow Alga Chlamydomonas nivalis During Temperature Fluctuations

“…CHLAMY1 is a circadian RBP in C. reinhardtii ( Iliev et al, 2006 ). CHLAMY1 C3 subunit interacts with two proteins, XRN1 and Musashi, which cooperate to confer thermal acclimation to C. reinhardtii ( Li et al, 2018 ). In our work, CHLAMY1 C3 subunit, XRN1, and Musashi were all upregulated in C. reinhardtii .…”

“…Another relevant clock protein, XRN1, a 5′–3′ exoribonuclease, interacts with the CHLAMY1 subunits ( Dathe et al, 2012 ). According to a recent study, the C3 subunit, XRN1, and Musashi interact with each other and cooperate to confer thermal acclimation to C. reinhardtii ( Li et al, 2018 ). In our analysis, the C3 subunit, XRN1, and Musashi were identified as DEGs in C. reinhardtii consistently with previous studies, but were not differentially regulated in C. nivalis .…”

Alternative Splice Variant Sheds Light on Temperature Acclimation in Algae

“…The interaction of C3 and XRN1 provides a direct integration of temperature and clock regulation, but may also involve other regulatory factors. Li et al (2018) sought to identify other factors working with CHLAMY1 by conducting a coimmunoprecipitation experiment using C. reinhardtii extract and XRN1 as bait. In addition to C3, the authors discovered a number of novel interacting RNA-binding proteins, including one called Musashi.…”

“…Understanding mechanisms of temperature acclimation is becoming more important with changes in global climate and increases in ocean temperatures. Li et al (2018) have identified a new component in the temperature acclimation system in microalgae through characterization of an alternatively spliced variant, Musashi 60 kD, and have demonstrated its function under physiological conditions. The putative roles of the other Musashi alternatively spliced variants are unknown but common to RNA-binding proteins (Cho et al, 2015).…”