Abstract
The floral transition stage is pivotal for sustaining plant populations and is affected by several environmental factors, including photoperiod. However, the mechanisms underlying photoperiodic flowering responses are not fully understood. Herein, we have shown that exposure to an extended photoperiod effectively induced early flowering in Arabidopsis plants, at a range of different nitrate concentrations. However, these photoperiodic flowering responses were attenuated when the nitrate levels were suboptimal for flowering. An extended photoperiod also improved the root nitrate uptake of by NITRATE TRANSPORTER 1.1 (NRT1.1) and NITRATE TRANSPORTER 2.1 (NRT2.1), whereas the loss of function of NRT1.1/NRT2.1 in the nrt1.1-1/2.1-2 mutants suppressed the expression of the key flowering genes CONSTANS (CO) and FLOWERING LOCUS T (FT), and reduced the sensitivity of the photoperiodic flowering responses to elevated levels of nitrate. These results suggest that the upregulation of root nitrate uptake during extended photoperiods, contributed to the observed early flowering. The results also showed that the sensitivity of photoperiodic flowering responses to elevated levels of nitrate, were also reduced by either the replacement of nitrate with its assimilation intermediate product, ammonium, or by the dysfunction of the nitrate assimilation pathway. This indicates that nitrate serves as both a nutrient source for plant growth and as a signaling molecule for floral induction during extended photoperiods.
Highlights
The transition from vegetative to reproductive development is a pivotal event in the lives of annual plants and can have a profound impact on their fertility and population sustainability (Guo and Yang, 1998; Lin and Tsay, 2017)
We first evaluated the effects of different nitrate supplies (∼1 mM) on flowering in Arabidopsis thaliana ecotype Col-0 plants to clarify the effects of nitrate availability on flowering under the growth conditions used in this study
These results suggest that the flowering of Arabidopsis plants is promoted by increasing the nitrate availability, but only below an optimal level, under both LD and SD conditions
Summary
The transition from vegetative to reproductive development is a pivotal event in the lives of annual plants and can have a profound impact on their fertility and population sustainability (Guo and Yang, 1998; Lin and Tsay, 2017). Srikanth and Schmid, 2011; Kim et al, 2012; Wahl et al, 2013; Capovilla et al, 2014; Yuan et al, 2016; Luo et al, 2018; Andrés et al, 2020; Bao et al, 2020). These pathways were found to converge on the “integrator” genes SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) and FLOWERING LOCUS T (FT) (Putterill et al, 1995; Luo et al, 2018; Andrés et al, 2020). Chromatin immunoprecipitation experiments have shown that SMZ can directly bind to the FT locus, which leads to the downregulation of FT expression (Mathieu et al, 2009; Golembeski and Imaizumi, 2015)
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