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bioRxiv · 10.1101/2022.03.09.483716

A chronotype effect: circadian-period variation underlies the local adaptation of photoperiodism in the short-day plant Lemna aequinoctialis.

Muranaka, T.·Ito, S.·Kudoh, H.·Oyama, T.
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Abstract

Phenotypic variation is the basis for trait adaptation via evolutionary selection.1, 2, 3 However, the driving forces behind the quantitative trait variations remain unclear owing to their complexity at the molecular level.4, 5, 6 This study focused on the natural variation of the free-running period (FRP) of the circadian clock because FRP is a determining factor of the internal clock phase (chronotype), which is responsible for physiological timing during a day.7 Although natural variations in FRP have been widely reported,8, 10, 11 few studies have shown the association between FRP and adaptive temporal traits. As a clock-dependent physiological process, photoperiodism is a typical target of local adaptation.12, 13 Lemna aequinoctialis in Japan is a paddy-field duckweed exhibiting a latitudinal cline of critical day-lengths (CDLs) for short-day flowering.14 To investigate the relationship between FRP and CDL, we collected 72 strains of L. aequinoctialis within a latitudinal range between 31.5{degrees}N to 43.8{degrees}N. We found a significant correlation (P = 7.5E-8) between FRPs and locally adaptive CDLs, confirming that the variation in FRP-dependent chronotypes underlies geographically differentiated photoperiodism. Diel transcriptome analysis revealed that the induction timing of a florigen gene is key for connecting chronotypes to photoperiodism at the molecular level. Based on these results, we propose a fundamental rule concerning the "chronotype effect" in evolution: the variation of FRP functions as a resource for the variation of temporal traits. This study highlights the adaptive significance of FRP variation and provides a reason for the maintenance of FRP variation in natural populations.

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Muranaka, T., Ito, S., Kudoh, H., Oyama, T.. 2022-03-12. A chronotype effect: circadian-period variation underlies the local adaptation of photoperiodism in the short-day plant Lemna aequinoctialis.. https://doi.org/10.1101/2022.03.09.483716

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