March 2022 ESRFnews 17

STRUCTURAL BIOLOGY

Jon Cartwright

EVIDENCE OF EARLY SPRING

residues. Prion-like domains such as this have already been considered as the mediators of environmental response in yeast; and when Zubieta and Hutin s collabo- rators engineered A. thaliana to express a version of ELF3 without its prion-like domain, it resisted early flower- ing under warmer conditions, implying that the domain has a critical role. Further tests demonstrated that the original ELF3 appears to undergo condensation at about 28 °C, ceasing to be evenly dispersed within cells and self- assembling into droplets, like oil in water (Nature 585 256). Could condensation be the secret to early flower-

ing? It is a trendy concept in biophysics, and Hutin is wary of overusing it. Recently in the literature, almost every speckle is called phase separation, she says. Yet it would explain why the evening complex struggles to bind to DNA at higher temperatures. To investigate it in detail, the researchers employed a raft of complementary techniques, including small-angle scattering in various conditions at the ESRF s dedicated bioSAXS beamline, BM29. That s one of the nicest techniques to study proteins in solution, says Hutin, who performed most of the experiments. We collaborate with [BM29 beamline scientist] Mark Tully really well, and we ve worked at the beamline now for several years so we ve had the possibility to partially adapt it to our needs, using different protein purification methods, microfluidics pipelines and so on. In parallel, we can also see the same sample using X-ray diffraction to get an overview of long-range ordering of molecules in the solid phase. The measurements allowed Zubieta and Hutin to expose

the dynamics and structure of the condensed and non- condensed prion-like domain of ELF3 as a function of pH and temperature. In fact, as the measurements showed, the protein domain has not two but three phases: a non-

condensed, dilute phase of globular oligomers; a condensed phase exhibiting extended polypeptide chains; and finally a gel exhibiting highly ordered and stacked molecules. Impor- tantly, by varying the length of long repetitive stretches of amino acids, known as polyQ repeats, in the domain, the researchers could tune the temperature at which conden- sation and, in principle, flowering occurs. We think phase separation is one way a plant perceives temperature, says Zubieta. And since it can be tuned to occur at different temperatures, it may be important in different species that grow in different climates.

The researchers are still a long way from engineering plants to be resilient to climate change. Before working on crops, they need to test their findings in other model plant systems, by creating a series of ELF3 mutants in an attempt to vary the temperature of phase separation. But the results so far have been very promising. In a warming world, we will need all the tools at our disposal to counter- act the effects of climate change on crop plants, says Zubieta. Understanding and tuning the sensing mecha- nisms plants use to interact with their environment may be one key to long-term food security. 

The researchers employed a raft of complementary techniques at the ESRF s specialist bioSAXS

beamline, BM29

winter

spring

18401820 1860 1880 1900 1920 1940 1960 1980 2000 2020

15 April

1 April

15 March

1 March

15 February

1 February

15 January

1 January

2nd horse chestnut

1st horse chestnut

3rd horse chestnut

4th horse chestnut

In Geneva, data have been collected since 1818 on the arrival of the first leaf of a horse chestnut tree (the marronier officiel) that is an official harbinger of spring in Switzerland. Over the years, as one tree has died another has been grown to replace it. The graph plots the leaves arriving earlier and earlier in the year, demonstrating the effects of recent global warming.

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