The Role of the miR399-PHO2 Module in the Regulation of Flowering Time in Response to Different Ambient Temperatures in Arabidopsis thaliana

Abstract

A moderate change in ambient temperature significantly affects plant physiology including flowering time. MiR399 and its target gene PHOSPHATE 2 (PHO2) are known to play a role in the maintenance of phosphate homeostasis. However, the regulation of flowering time by the miR399-PHO2 module has not been investigated. As we have previously identified miR399 as an ambient temperature-responsive miRNA, we further investigated whether a change in expression of the miR399-PHO2 module affects flowering time in response to ambient temperature changes. Here, we showed that miR399b-overexpressing plants and a loss-of-function allele of PHO2 (pho2) exhibited an early flowering phenotype only at normal temperature (23°C). Interestingly, their flowering time at lower temperature (16°C) was similar to that of wild-type plants, suggesting that alteration in flowering time by miR399 and its target PHO2 was seen only at normal temperature (23°C). Flowering time ratio (16°C/23°C) revealed that miR399b-overexpressing plants and pho2 mutants showed increased sensitivity to ambient temperature changes. Expression analysis indicated that expression of TWIN SISTER OF FT (TSF) was increased in miR399b-overexpressing plants and pho2 mutants at 23°C, suggesting that their early flowering phenotype is associated with TSF upregulation. Taken together, our results suggest that miR399, an ambient temperature-responsive miRNA, plays a role in ambient temperature-responsive flowering in Arabidopsis.

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“…Relative abundance of the transcripts was calculated by the statistical formula from geNorm (Vandesompele et al, 2002). For reference genes for quantification by RT-qPCR, two stably expressed genes [PP2AA3 (AT1G13320) and SAND family protein (AT2G28390)] were used to follow the 'The eleven golden rules for quantitative RT-PCR' (Kim et al, 2011;Udvardi et al, 2008). All RT-qPCR experiments were carried out in two or three biological replicates (independently harvested samples at different days) with three technical triplicates, each with similar results.…”

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