The spliceosome assembly factor GEMIN2 attenuates the effects of temperature on alternative splicing and circadian rhythms

Abstract

The mechanisms by which poikilothermic organisms ensure that biological processes are robust to temperature changes are largely unknown. Temperature compensation, the ability of circadian rhythms to maintain a relatively constant period over the broad range of temperatures resulting from seasonal fluctuations in environmental conditions, is a defining property of circadian networks. Temperature affects the alternative splicing (AS) of several clock genes in fungi, plants, and flies, but the splicing factors that modulate these effects to ensure clock accuracy throughout the year remain to be identified. Here we show that GEMIN2, a spliceosomal small nuclear ribonucleoprotein assembly factor conserved from yeast to humans, modulates low temperature effects on a large subset of pre-mRNA splicing events. In particular, GEMIN2 controls the AS of several clock genes and attenuates the effects of temperature on the circadian period in Arabidopsis thaliana. We conclude that GEMIN2 is a key component of a posttranscriptional regulatory mechanism that ensures the appropriate acclimation of plants to daily and seasonal changes in temperature conditions. spliceosome assembly | alternative splicing | circadian rhythms | Arabidopsis | GEMIN2 C ircadian clocks allow organisms to coordinate physiological processes with periodic environmental changes. The core of all circadian systems, in organisms ranging from cyanobacteria to humans, is a network of multiple interlocked feedback loops that operate at the transcriptional, translational, and posttranslational levels to sustain oscillations with a period of ∼24 h, even in the absence of environmental cues. An increasing body of evidence links alternative splicing (AS) with the regulation of circadian networks across eukaryotic organisms (1-3). The core clock genes period in Drosophila, frequency in Neurospora, and BMAL2 in humans undergo AS to give rise to different mRNA isoforms (1, 2, 4). In Arabidopsis, several core clock genes, including TIMING OF CAB EXPRESSION 1 (TOC1) and CIRCA-DIAN CLOCK ASSOCIATED 1 (CCA1), also undergo extensive AS (5-7).Interestingly, many of the alternative mRNA isoforms associated with the Arabidopsis core clock genes are abundant or alter their abundance upon changes in environmental conditions, suggesting that they have important physiological roles (5-7). For example, there is strong evidence that temperature regulation of CCA1 AS is critical for the proper functioning of circadian rhythms under cold conditions (8). Temperature also regulates the AS of frequency in Neurospora and period in Drosophila (1, 2), thereby promoting the proper functioning of circadian networks under the wide range of temperatures occurring throughout the seasons. Although our knowledge of the transcription factors that regulate clock function in different organisms has increased drastically over the last two decades, the splicing factors that modulate the AS patterns of core clock genes are only starting to be characterized (1). Splicing factors that mediate the effects...

How does temperature affect splicing events? Isoform switching of splicing factors regulates splicing of LATE ELONGATED HYPOCOTYL (LHY)

“…Mutations in the SICKLE ( SIC ) gene, which encodes a nuclear protein implicated in the control of AS, markedly stimulate the accumulation of splice variants of LHY and other clock genes at cool temperatures (Marshall, Tartaglio, Duarte, & Harmon, ). Moreover, sic mutants and mutants in other splicing‐related genes, including for the spliceosomal components GEMIN2 and SKIP , affect the period of the circadian clock (Hernando, Sanchez, Mancini, & Yanovsky, ; Jones et al, ; Marshall et al, ; Sanchez et al, ; Schlaen et al, ; Wang et al, ). Notably, sic , skip , and gemin2 mutants are also impaired in temperature compensation, a defining feature of circadian clocks whereby the pace of the clock is largely unaffected across a range of physiologically relevant temperatures (Pittendrigh, ).…”

Alternative Splicing of Barley Clock Genes in Response to Low Temperature

“…The splicing factor SKIP regulates the alternative splicing of circadian clock genes in a temperature-sensitive manner, and mutations in SKIP lengthen the circadian period [40]. More recently, analyses of a mutation in the GEMIN2 gene has shown that this spliceosomal factor modulates low temperature AS of several clock genes required for proper temperature compensation [18]. Most plant clock studies use Arabidopsis such that our knowledge of the evolution and conservation of AS regulation of circadian clock gene expression in response to temperature is limited.…”

Global spatial analysis of Arabidopsis natural variants implicates 5′UTR splicing of LATE ELONGATED HYPOCOTYL in responses to temperature

“…Precisely how temperature information is perceived and transduced to the clock via post‐transcriptional mechanisms is an area of speculation and how this might mechanistically coordinate gating of output pathways is not known. Similarly, it remains unclear to what extent temperature‐associated clock AS is mechanistically linked to inherently important core clock phenomena such as temperature compensation or temperature entrainment of the clock (Edwards et al, ; Edwards, Lynn, Gyula, Nagy, & Millar, ; Salome & McClung, ), although it is notable that splicing related components such as SICKLE , GEMIN2 , and SKIP are implicated in temperature compensation (Marshall, Tartaglio, Duarte, & Harmon, ; Schlaen et al, ; Wang et al, ).…”