Overexpression of GSH1 gene mimics transcriptional response to low temperature during seed vernalization treatment of Arabidopsis.

Keeping imbibed seeds at low temperatures for a certain period, so-called seed vernalization (SV) treatment, promotes seed germination and subsequent flowering in various plants. Vernalization-promoting flowering requires GSH. However, we show here that increased GSH biosynthesis partially mimics SV treatment in Arabidopsis thaliana. SV treatment (keeping imbibed seeds at 4°C for 24 h) induced a specific pattern of gene expression and promoted subsequent flowering in WT A. thaliana. A similar pattern was observed at 22°C in transgenic (35S-GSH1) plants overexpressing the γ-glutamylcysteine synthetase gene GSH1, coding for an enzyme limiting GSH biosynthesis, under the control of the cauliflower mosaic virus 35S promoter. This pattern of gene expression was further strengthened at 4°C and indistinguishable from the WT pattern at 4°C. However, flowering in 35S-GSH1 plants was less responsive to SV treatment than in WT plants. There was a difference in the transcript behavior of the flowering repressor FLC between WT and 35S-GSH1 plants. Unlike other genes responsive to SV treatment, the SV-dependent decrease in FLC in WT plants was reversed in 35S-GSH1 plants. SV treatment increased the GSSG level in WT seeds while its level was high in 35S-GSH1 plants, even at a non-vernalizing temperature. Taking into consideration that low temperatures stimulate GSH biosynthesis and cause oxidative stress, GSSG is considered to trigger a low-temperature response, although enhanced GSH synthesis was not enough to completely mimic the SV treatment.

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