S‐Nitrosoglutathione works downstream of nitric oxide to mediate iron‐deficiency signaling in Arabidopsis

Abstract

Iron (Fe) is essential for plant growth and development. Knowledge of Fe signaling, from the beginning of perception to activation of the uptake process, is critical for crop improvement. Here, by using chemical screening, we identified a small molecule 3-amino-N-(3-methylphenyl)thieno[2,3-b]pyridine-2-carboxamide named R7 ('R' denoting repressor of IRON-REGULATED TRANSPORTER 1), that modulates Fe homeostasis of Arabidopsis. R7 treatment led to reduced Fe levels in plants, thus causing severe chlorosis under Fe deficiency. Expression analysis of central transcription factors, FER-LIKE IRON DEFICIENCY INDUCED TRANSCRIPTION FACTOR (FIT) and subgroup Ib basic helix-loop-helix (Ib bHLH) genes bHLH38/39/100/101, revealed that R7 targets the FIT-dependent transcriptional pathway. Exogenously supplying S-nitrosoglutathione (GSNO), but not other nitric oxide (NO) donors sodium nitroprusside (SNP) and S-nitroso-N-acetyl-dl-penicillamine (SANP), alleviated the inhibitory effects of R7 on Fe homeostasis. R7 did not inhibit cellular levels of NO or glutathione but decreased GSNO level in roots. We demonstrate that NO is involved in regulating not only the FIT transcriptional network but also the Ib bHLH networks. In addition, GSNO, from S-nitrosylation of glutathione, specifically mediates the Fe-starvation signal to FIT, which is distinct from the NO to Ib bHLH signal. Our work dissects the molecular connection between NO and the Fe-starvation response. We present a new signaling route whereby GSNO acts downstream of NO to trigger the Fe-deficiency response in Arabidopsis.

A Shoot Fe Signaling Pathway Requiring the OPT3 Transporter Controls GSNO Reductase and Ethylene in Arabidopsis thaliana Roots

“…Similarly to ethylene, GSH ( Table 2 ) and NO also increase in Fe-deficient WT roots, where they have been implicated in the activation of Fe deficiency responses ( Zaharieva and Abadía, 2003 ; Zaharieva et al, 2004 ; Graziano and Lamattina, 2007 ; Bacaicoa et al, 2009 ; Chen et al, 2010 ; García et al, 2011 ; Koen et al, 2012 ; Shanmugam et al, 2015 ; Kailasam et al, 2018 ). However, results in this work show that GSNO content in WT roots, in contrast to its precursors GSH and NO, decreases upon Fe deficiency ( Figures 10 , 11 ), which agrees with previous results ( Shanmugam et al, 2015 ; Kailasam et al, 2018 ). Since GSNOR reduces GSNO to GSSG and other byproducts, like hydroxylamine and H 3 N ( Leterrier et al, 2011 ; Corpas et al, 2013 ; Kubienová et al, 2014 ), we wanted to know whether GSNOR increases in Fe deficient roots.…”

“…Among them are auxin, ethylene, salicylic acid, nitric oxide (NO), sucrose, and glutathione (GSH). All of them increase in Fe-deficient roots although their precise roles and interactions are not totally known ( Zaharieva and Abadía, 2003 ; Zaharieva et al, 2004 ; Lucena et al, 2006 , 2015 ; Graziano and Lamattina, 2007 ; Waters et al, 2007 ; Bacaicoa et al, 2009 , 2011 ; Chen et al, 2010 ; García et al, 2010 , 2011 ; Lingam et al, 2011 ; Meiser et al, 2011 ; Romera et al, 2011 , 2017 ; Koen et al, 2012 ; Yang et al, 2014 ; Shanmugam et al, 2015 ; Lin et al, 2016 ; Shen et al, 2016 ; Li and Lan, 2017 ; Kailasam et al, 2018 ). There are also some hormones, such as cytokinins and jasmonates, that have been involved in the suppression of Fe deficiency responses ( Séguéla et al, 2008 ; Maurer et al, 2011 ).…”

“…Both GSH and NO increase in roots under Fe deficiency and have been implicated in the activation of Fe responses ( Zaharieva and Abadía, 2003 ; Zaharieva et al, 2004 ; Graziano and Lamattina, 2007 ; Bacaicoa et al, 2009 ; Chen et al, 2010 ; García et al, 2011 ; Koen et al, 2012 ; Shanmugam et al, 2015 ; Kailasam et al, 2018 ). However, S -nitrosoglutathione (GSNO), the most abundant low-molecular-weight S -nitrosothiol in plants ( Liu et al, 2018 ), and which is derived from GSH and NO ( Corpas et al, 2013 ), decreases under Fe deficiency in Arabidopsis roots ( Shanmugam et al, 2015 ; Kailasam et al, 2018 ). Since GSNOR regulates GSNO content by decomposing it to oxidized glutathione (GSSG) and H 3 N ( Leterrier et al, 2011 ; Corpas et al, 2013 ), we wanted to know whether GSNOR increases in roots under Fe deficiency.…”

A HemK class glutamine‐methyltransferase is involved in the termination of translation and essential for iron homeostasis in Arabidopsis

“…Luminescence imaging was performed according to Kailasam et al . (). Putative candidate mutants were advanced for M 3 generation.…”

“…Arabidopsis thaliana Col‐0, Landsberg erecta (L er ), T‐DNA mutant nrf1‐2 (Salk_027510) and ProIRT1:LUC reporter plants (Kailasam et al , ) were used. Seeds were surface‐sterilized and stratified for 2 d at 4°C.…”