The starting point for this work was the idea that the 5’UTR of the core clock gene LATE ELONGATED HYPOCOTYL, also known as LHY, could function as a thermosensor given that we previously saw temperature sensitive alternative splicing of LHY.
We tested our theory using the 1001 genomes resource, a whole-genome sequence database for at least 1001 strains of the reference plant, Arabidopsis thaliana. Arabidopsis is native to Europe, but can now be found in the United States, North Africa and temperate Asia. We examined subtle differences, or polymorphisms, in the DNA sequences of >1001 accessions. These are often referred to as single nucleotide polymorphisms (SNPs). We found that different strains tended to ‘shake out’ as particular ordered assemblies of the SNPs, called haplotypes [for example, in the picture above the G/G/U/G/C haplotype is compared to the A/U/G/C/A haplotype] .
We were interested to see if the distinct haplotypes aligned with particular features of where these plants were growing – maybe the haplotypes grouped according to latitude, longitude, or altitude? Or would they group according to climate, such as temperature? seasonality? or even rainfall? For this we made use of the WorlClim database – a free public resource offering global climate data for ecological modelling.
The key findings were that:
One of the haplotypes has hallmarks of being a signature of ‘relict’ accessions (survivors of the last ice-age and the subsequent expansion of new populations). This version is the most distinct in the respect that, worldwide, the accessions bearing this haplotype are found in regions of low rainfall. They are also associated with the highest elevations with low mean annual temperatures and a wider range of maximum–minimum temperatures
Two of the remaining three haplotypes seem to associate with milder annual mean temperatures and lower altitude and wetter habitats
The fourth haplotype, seems to be a low temperature specialist. This haplotype is commonly found in the mountainous Pyrenees region of northern Spain and is prominent at the limit of Arabidopsis growth in northern Sweden
By measuring the extent of LHY spliced upon cooling in representative strains from two haplotypes we established that haplotype does indeed affect the splicing of LHY transcripts in response to cooling
We propose that the LHY haplotypes possess distinct 5′UTR pre‐mRNA folding thermodynamics and/or specific biological stabilities based around the binding of trans‐acting RNA splicing factors
There is much interest in identifying plant thermometers and how they have evolved to cope with new temperature environments. Our new work shows that subtle differences in the DNA sequence of global populations of Arabidopsis plants influences the scalable splicing sensitivity of the mRNA for this central clock component, thereby finely tuning the clock to specific temperature environments.
We anticipate that these findings will be of interest and relevant to crop breeding programs that aim to produce stable food crops in the face of changing climate.