Patterns of circadian clock gene expression at different temperatures relate to Nothofagus species distribution across different thermal environments in Patagonia

ESTRAVIS-BARCALA, M; CAGNACCI, J; HEER, K; ARANA, MV; BELLORA, N; GONZALEZ POLO, M; OPGHENOORTH, L; MARTINEZ-MEIER, A; ZIEGENHAGEN, B; YANOVSKY, M

Congreso; Plant Biology; 2019

Circadian clock increases organisms´ fitness by providing a mechanism to anticipate events such as sunrise and adjust their transcriptional programs. Due to its ability to maintain 24h-rhythms over a wide range of temperatures (property of compensation by temperature), circadian clocks have been proposed to contribute to thermal adaptation and plasticity in plants. However, consequences of clock performance on plant behavior in natural ecosystems are scarcely known. Here we show that circadian clock of Nothofagus obliqua and N. pumilio, two emblematic tree species of the sub-Antarctic Patagonian forests, lose their property of compensation by temperature at 34°C. These species constitute examples of extremes of adaptation to altitude, inhabiting non-overlapping thermal niches. Moreover, at 31°C, daily oscillation in the expression of the homolog clock gene NoTOC1 is maintained in N. obliqua, which inhabits warmer and lower altitudes in the mountain but is lost in N. pumilio, which inhabits higher and colder habitats. In the latter, warm temperatures exert a strong effect on its transcriptome. Experiments in an old-growth temperate forest show that the performance of the clock of N. pumilio, measured as the expression of NpTOC1, is affected in warmer and lower environments out of its distribution range, indicating that clock functioning is susceptible to warm temperatures, and this is associated with reduced accumulation of dry weight, chlorophylls and survival of the seedlings. This behavior is not evident in N. obliqua seedlings grown in colder environments in higher environments out of its natural ecological range. Taken together, our results provide the first evidences in favor that differences between plant species in the influence of temperature on the performance of their circadian clocks are the bases for physiological adaptation to the local thermic environment and therefore for differences in altitudinal distribution.