Nitric Oxide Functions as a Signal and Acts Upstream of AtCaM3 in Thermotolerance in Arabidopsis Seedlings    

Abstract

To characterize the role of nitric oxide (NO) in the tolerance of Arabidopsis (Arabidopsis thaliana) to heat shock (HS), we investigated the effects of heat on three types of Arabidopsis seedlings: wild type, noa1(rif1) (for nitric oxide associated1/resistant to inhibition by fosmidomycin1) and nia1nia2 (for nitrate reductase [NR]-defective double mutant), which both exhibit reduced endogenous NO levels, and a rescued line of noa1(rif1). After HS treatment, the survival ratios of the mutant seedlings were lower than those of wild type; however, they were partially restored in the rescued line. Treatment of the seedlings with sodium nitroprusside or S-nitroso-N-acetylpenicillamine revealed that internal NO affects heat sensitivity in a concentrationdependent manner. Calmodulin 3 (CaM3) is a key component of HS signaling in Arabidopsis. Real-time reverse transcriptionpolymerase chain reaction analysis after HS treatment revealed that the AtCaM3 mRNA level was regulated by the internal NO level. Sodium nitroprusside enhanced the survival of the wild-type and noa1(rif1) seedlings; however, no obvious effects were observed for cam3 single or cam3noa1(rif1) double mutant seedlings, suggesting that AtCaM3 is involved in NO signal transduction as a downstream factor. This point was verified by phenotypic analysis and thermotolerance testing using seedlings of three AtCaM3-overexpressing transgenic lines in an noa1(rif1) background. Electrophoretic mobility-shift and western-blot analyses demonstrated that after HS treatment, NO stimulated the DNA-binding activity of HS transcription factors and the accumulation of heat shock protein 18.2 (HSP18.2) through AtCaM3. These data indicate that NO functions in signaling and acts upstream of AtCaM3 in thermotolerance, which is dependent on increased HS transcription factor DNAbinding activity and HSP accumulation.

SNF1-Related Protein Kinases Type 2 Are Involved in Plant Responses to Cadmium Stress

“…To investigate whether the activation is due to NO produced via the NR or AtNOA1 pathways, we studied Cd 2+ -dependent SnRK2 activation in hydroponically grown seedlings of nia1nia2 (double knockout mutant of NR) and atnoa1 Arabidopsis T-DNA insertion mutants. The atnoa1 and nia1nia2 mutants had previously been shown to produce less NO in response to several biotic as well as abiotic stresses (Besson-Bard et al, 2008;Zhao et al, 2009;Hao et al, 2010;Lozano-Juste and León, 2010;Sun et al, 2010;Xuan et al, 2010). In both nia1nia2 and atnoa1 seedlings, we observed activation of SnRK2(s) in response to CdCl 2 treatment (Fig.…”

Hydrogen Peroxide Acts Upstream of Nitric Oxide in the Heat Shock Pathway in Arabidopsis Seedlings

“…Nitric oxide (NO) is a bioactive molecule that is extensively involved in plant defenses against environmental stimuli, including drought, salt, cold, heat, and disease (Zhao et al, 2004;Guo and Crawford, 2005;Neill et al, 2008;Wilson et al, 2008;Xuan et al, 2010). NO is mainly produced via two pathways: the Arg-dependent nitric oxide synthase (NOS) and nitrite-dependent nitrate reductase (NR) pathways.…”

Membrane lipid composition affects plant heat sensing and modulates Ca2+-dependent heat shock response

“…[8][9][10] Yet, the overexpression of HSPs, so called the heat shock response (HSR), can be activated under mild physiological conditions that are unlikely to cause any protein denaturation in the cell. [11][12][13] Although multiple HSR triggering mechanisms may co-exist, 6,[14][15][16] recent evidences in bacteria, algae, plants and mammalian cells point at the understanding how plants sense and respond to heat stress is central to improve crop tolerance and productivity. recent findings in Physcomitrella patens demonstrated that the controlled passage of calcium ions across the plasma membrane regulates the heat shock response (hSr).…”