Transgenerational adaptation to heavy metal salts in Arabidopsis

Mohammad Rahavi

doi:10.3389/fpls.2011.00091

Abstract

Exposure to abiotic and biotic stress results in changes in plant physiology and triggers genomic instability. Recent reports suggest that the progeny of stressed plants also exhibit changes in genome stability, stress tolerance, and methylation. Here we analyzed whether exposure to Ni2+, Cd2+, and Cu2+ salts leads to transgenerational changes in homologous recombination frequency and stress tolerance. We found that the immediate progeny of stressed plants exhibited an increased rate of recombination. However, when the progeny of stressed plants was propagated without stress, recombination reverted to normal levels. Exposure of plants to heavy metals for five consecutive generations (S1–S5) resulted in recombination frequency being maintained at a high level. Skipping stress following two to three generations of propagation with 50 mM Ni2+ or Cd2+ did not decrease the recombination frequency, suggesting plant acclimation to upregulated recombination. Analysis of the progeny of plants exposed to Cu2+ and Ni2+ indicated higher stress tolerance to the heavy metal parental plants were exposed to. Tolerance was higher in plants propagated with stress for three to five generations, which resulted in longer roots than plants propagated on heavy metals for only one to two generations. Tolerance was also more prominent upon exposure to a higher concentration of salts. The progeny of stressed plants were also more tolerant to NaCl and methyl methane sulfonate.

Highlights

Stress exposure results in numerous physiological changes in plants (Wilkinson and Davies, 2010; Roy et al, 2011)
Several recent reports have demonstrated that in addition to higher stress tolerance the progeny of stressed plants exhibit changes in DNA methylation and genome stability (Molinier et al, 2005; Boyko and Kovalchuk, 2008; Pecinka et al, 2009; Boyko et al, 2010a; Kathiria et al, 2010; Ito et al, 2011; Yao and Kovalchuk, 2011) which appear to be dependent on the function of short interferingRNAs -regulated pathways. siRNAs are trans-acting epigenetic signals that can reversibly and in a sequence-specific manner modify gene expression at the transcriptional level (Carthew and Sontheimer, 2009; Malone and Hannon, 2009)
Roots were longer in S3–S5 generations than S1–S2, and the difference between S1–S5 and S0 plants was more prominent upon exposure to a higher concentration (200 mM) of heavy metal salt (Figure 5)

Summary

INTRODUCTION

Stress exposure results in numerous physiological changes in plants (Wilkinson and Davies, 2010; Roy et al, 2011). Skipping two generations of stress exposure returned HRF back to normal levels in most of the cases, with the exception of G5 plants exposed to 50 mM Cd2+ and G4–G5 plants exposed to 100 mM of Ni2+ These experiments confirmed that maintenance of high recombination frequency through a number of generations requires constant exposure to stress. Roots were longer in S3–S5 generations than S1–S2, and the difference between S1–S5 and S0 plants was more prominent upon exposure to a higher concentration (200 mM) of heavy metal salt (Figure 5) These experiments indicated that the progeny of stressed plants acquire higher tolerance to the same stress. The analysis of root length in plants exposed to NaCl showed that roots were longer in the progeny of stressed plants, a difference that was more severe as a result of exposure to 125 mM than to 75 mM NaCl (Figure 6). Exposure to 135 ppm MMS resulted in severe growth inhibition and the majority of plants either did not germinate or died at the cotyledon stage, not allowing for any meaningful comparison

DISCUSSION

MATERIALS AND METHODS