Geomagnetic Field (Gmf) and Plant Evolution: Investigating the Effects of Gmf Reversal on <em>Arabidopsis thaliana </em>Development and Gene Expression

Abstract

One of the most stimulating observations in plant evolution is a correlation between the occurrence of geomagnetic field (GMF) reversals (or excursions) and the moment of the radiation of Angiosperms. This led to the hypothesis that alterations in GMF polarity may play a role in plant evolution. Here, we describe a method to test this hypothesis by exposing Arabidopsis thaliana to artificially reversed GMF conditions. We used a three-axis magnetometer and the collected data were used to calculate the magnitude of the GMF. Three DC power supplies were connected to three Helmholtz coil pairs and were controlled by a computer to alter the GMF conditions. Plants grown in Petri plates were exposed to both normal and reversed GMF conditions. Sham exposure experiments were also performed. Exposed plants were photographed during the experiment and images were analyzed to calculate root length and leaf areas. Arabidopsis total RNA was extracted and Quantitative Real Time-PCR (qPCR) analyses were performed on gene expression of CRUCIFERIN 3 (CRU3), copper transport protein1 (COTP1), Redox Responsive Transcription Factor1 (RRTF1), Fe Superoxide Dismutase 1, (FSD1), Catalase3 (CAT3), Thylakoidal Ascorbate Peroxidase (TAPX), a cytosolic Ascorbate Peroxidase1 (APX1), and NADPH/respiratory burst oxidase protein D (RbohD). Four different reference genes were analysed to normalize the results of the qPCR. The best of the four genes was selected and the most stable gene for normalization was used. Our data show for the first time that reversing the GMF polarity using triaxial coils has significant effects on plant growth and gene expression. This supports the hypothesis that GMF reversal contributes to inducing changes in plant development that might justify a higher selective pressure, eventually leading to plant evolution.

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

“…The verified delay in the transition to flowering caused by NNMF could be correlated to the observed speciation of Angiosperms after geomagnetic field reversals [Maffei, 2014;Occhipinti et al, 2014;Bertea et al, 2015], which does not exclude a hypothetical influence of GMF magnitude and polarity on plant evolution on a geological time-scale.…”

“…These events are followed by the progressive reduction of gibberellin pathway downregulation. Our results indicate that NNMF do not prevent flowering, and that variations of the MF are sufficient to modulate specific genes in the early stages of flower induction that are associated with the observed delay. The verified delay in the transition to flowering caused by NNMF could be correlated to the observed speciation of Angiosperms after geomagnetic field reversals [Maffei, ; Occhipinti et al, ; Bertea et al, ], which does not exclude a hypothetical influence of GMF magnitude and polarity on plant evolution on a geological time‐scale. Since GMF magnitude is not equal everywhere on the Earth's surface, it is possible that changes in GMF in different places could influence plant growth and reproduction. However, since the results on gene expression regulation described in this work might not reflect post‐translational modifications that lead to the production of proteins involved in flowering control, further proteomics studies are underway to better assess the role of NNMF on flowering control. Finally, experiments with one or more knock‐out mutants of the genes of interest, measuring expression levels in these genotypes, will provide further insight into the nature of triggering events and signal transduction.…”

“…1). This apparatus was also instrumental in our assessment of the effect of GMF reversal on A. thaliana gene expression [Bertea et al, 2015].…”

The Geomagnetic Field Is a Contributing Factor for an Efficient Iron Uptake in Arabidopsis thaliana

“…Furthermore, changes in the hormone levels, for instance, auxin and gibberellin, as well as a delay in flowering time have also been observed under near null MF (NNMF) conditions (Xu et al, 2012(Xu et al, , 2017(Xu et al, , 2018Agliassa et al, 2018a). Such delayed transition to flowering under NNMF is likely involved in the Angiosperms speciation during GMF reversals (Maffei, 2014;Occhipinti et al, 2014;Bertea et al, 2015), suggesting a possible contribution of the GMF magnitude on plant evolution.…”

“…In space programs, humans, animals and plants are introduced into magnetic environments with a decrease of MF intensity by about three orders of magnitude respect to GMF intensity (i.e., from about 35 µT to near 1 nT) (Maffei, 2014). Such condition is achievable by using GMF compensation systems such as the one we developed by using a triaxial Helmholtz coil (three computer-controlled orthogonal Helmholtz coils) (Bertea et al, 2015;Agliassa et al, 2018a). Our strategy to assess the role of the GMF on metal uptake in Arabidopsis seedlings was through the comparison of plants grown under either GMF or NNMF conditions.…”