Reduction of the geomagnetic field delays Arabidopsis thaliana flowering time through downregulation of flowering-related genes

Abstract

Variations in magnetic field (MF) intensity are known to induce plant morphological and gene expression changes. In Arabidopsis thaliana Col-0, near-null magnetic field (NNMF, i.e., <100 nT MF) causes a delay in the transition to flowering, but the expression of genes involved in this response has been poorly studied. Here, we showed a time-course quantitative analysis of the expression of both leaf (including clock genes, photoperiod pathway, GA20ox, SVP, and vernalization pathway) and floral meristem (including GA2ox, SOC1, AGL24, LFY, AP1, FD, and FLC) genes involved in the transition to flowering in A. thaliana under NNMF. NNMF induced a delayed flowering time and a significant reduction of leaf area index and flowering stem length, with respect to controls under geomagnetic field. Generation experiments (F₁ - and F₂ -NNMF) showed retention of flowering delay. The quantitative expression (qPCR) of some A. thaliana genes expressed in leaves and floral meristem was studied during transition to flowering. In leaves and flowering meristem, NNMF caused an early downregulation of clock, photoperiod, gibberellin, and vernalization pathways and a later downregulation of TSF, AP1, and FLC. In the floral meristem, the downregulation of AP1, AGL24, FT, and FLC in early phases of floral development was accompanied by a downregulation of the gibberellin pathway. The progressive upregulation of AGL24 and AP1 was also correlated to the delayed flowering by NNMF. The flowering delay is associated with the strong downregulation of FT, FLC, and GA20ox in the floral meristem and FT, TSF, FLC, and GA20ox in leaves. Bioelectromagnetics. 39:361-374, 2018. © 2018 The Authors. Bioelectromagnetics Published by Wiley Periodicals, Inc.

Keywords: Arabidopsis thaliana; delay in flowering time; geomagnetic field; leaves and floral meristem gene expression; near-null magnetic field.

Figure 1

Geomagnetic field compensation system. (A) Triaxial coils (comprised of a Helmholtz pair of octagonal coils for each of three perpendicular axes) for cancelling the geomagnetic field. (B) Example of a plot of residual MF measured by Bartington Fluxgate magnetometer during a near‐null MF experiment. (C) Same measurements, but during GMF. (D) Expected variations of magnetic inclination under NNMF. Inclination was defined as $\text{Arctan}\left(\frac{B_y}{\sqrt{B{x}^2+B{z}^2}}\right)$. The y‐axis was defined to run vertically, and x‐ and z‐axes were horizontal. MFS, magnetic field strength (mean values).

Figure 2

Effect of near‐null magnetic field (NNMF) on A. thaliana development and flowering time. (A) Phenological phases of A. thaliana development and flowering in plant exposed to GMF and to NNMF. (B) Leaf area index of plants exposed to normal (GMF) and NNMF. (C) Length of flowering stem in controls (GMF) and under NNMF. Metric bars indicate standard deviation; asterisks indicate significant (P < 0.05) differences between controls and NNMF. DAS, days after sowing. See also Supplementary Table S2.

Figure 3

Pattern of expression of genes involved in flowering in A. thaliana leaves. Cluster analysis was calculated by using Euclidean distances with median linkage. See text for description. DAS, days after sowing. Different shades of green and red correspond to expression levels reported in the figure color bar.

Figure 4

Pattern of expression of genes involved in flowering in A. thaliana floral meristem. The cluster analysis was calculated by using Euclidean distances with median linkage. See text for description. DAS, days after sowing. The different shades of green and red correspond to the expression levels reported in the figure color bar.

Figure 5

Schematic representation of gene expression patterns in A. thaliana leaves and floral meristem under near‐null magnetic field (NNMF). Leaf gene regulation of clock, photoperiod pathway, vernalization pathway, gibberellin pathway, and regulatory network is depicted during early, intermediate, and late stages of flowering according to data of Table 1. An early downregulation of clock, photoperiod, gibberellin, and vernalization pathways is accompanied by a downregulation of AP1 and GA20ox. In the floral meristem (data from Table 2), NNMF determines an early downregulation of the gibberellin pathway, AGL24 and AP1, with a significant upregulation of LFY, FD, and SVP. In both leaves and floral meristem data, upregulation is shown in green, downregulation in light red, and no regulation in white [Fornara et al., 2010; Jaeger et al., 2013; Valentim et al., 2015].