Flowering Plants

A single letter change in DNA code can potentially decide whether a plant is a lark or a night owl, according to a study published in the journal Plant, Cell and Environment.

Arabidopsis thaliana. Image credit: Carl Davies, CSIRO / CC BY 3.0.

Arabidopsis thaliana. Image credit: Carl Davies, CSIRO / CC BY 3.0.

The circadian clock is a temporal program found in organisms from all phyla. It is an adaptation to Earth’s rotation, conferring a 24-h structure on processes at all levels.

However, these entrainment signals are not consistent everywhere and vary with latitude, climate and seasonality. This leads to divergent selection for clocks which are locally adapted.

To investigate the genetic basis for this circadian variation, Dr. Hannah Rees of Earlham Institute and colleagues examined varying circadian rhythms in Swedish Arabidopsis plants.

“A plant’s overall health is heavily influenced by how closely its circadian clock is synchronized to the length of each day and the passing of seasons,” Dr. Rees said.

“An accurate body clock can give it an edge over competitors, predators and pathogens.”

“We were interested to see how plant circadian clocks would be affected in Sweden; a country that experiences extreme variations in daylight hours and climate.”

“Understanding the genetics behind body clock variation and adaptation could help us breed more climate-resilient crops in other regions.”

The researchers studied the genes in 191 different varieties of Arabidopsis obtained from across the whole of Sweden.

They were looking for tiny differences in genes between these plants which might explain the differences in circadian function.

The analysis revealed that a single DNA base-pair change in a specific gene, COR28, was more likely to be found in plants that flowered late and had a longer period length.

COR28 is a known coordinator of flowering time, freezing tolerance and the circadian clock; all of which may influence local adaptation in Sweden.

“It’s amazing that just one base-pair change within the sequence of a single gene can influence how quickly the clock ticks,” Dr. Rees said.

The scientists also used a pioneering delayed fluorescence imaging method to screen plants with differently-tuned circadian clocks.

They showed there was over 10 hours difference between the clocks of the earliest risers and latest phased plants — akin to the plants working opposite shift patterns.

Both geography and the genetic ancestry of the plant appeared to have an influence.

Arabidopsis thaliana is a model plant system,” Dr. Rees said.

“It was the first plant to have its genome sequenced and it’s been extensively studied in circadian biology, but this is the first time anyone has performed this type of association study to find the genes responsible for different clock types.”

“Our findings highlight some interesting genes that might present targets for crop breeders, and provide a platform for future research.”

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Hannah Rees et al. Naturally occurring circadian rhythm variation associated with clock gene loci in Swedish Arabidopsis accessions. Plant, Cell and Environment, published online November 11, 2020; doi: 10.1111/pce.13941

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