Abstract
Nitric oxide (NO) is involved in plant responses to many environmental stresses. Transgenic Arabidopsis lines that constitutively express rat neuronal NO synthase (nNOS) were described recently. In this study, it is reported that the nNOS transgenic Arabidopsis plants displayed high levels of osmolytes and increased antioxidant enzyme activities. Transcriptomic analysis identified 601 or 510 genes that were differentially expressed as a consequence of drought stress or nNOS transformation, respectively. Pathway and gene ontology (GO) term enrichment analyses revealed that genes involved in photosynthesis, redox, stress, and phytohormone and secondary metabolism were greatly affected by the nNOS transgene. Several CBF genes and members of zinc finger gene families, which are known to regulate transcription in the stress response, were changed by the nNOS transgene. Genes regulated by both the nNOS transgene and abscisic acid (ABA) treatments were compared and identified, including those for two ABA receptors (AtPYL4 and AtPYL5). Moreover, overexpression of AtPYL4 and AtPYL5 enhanced drought resistance, antioxidant enzyme activity, and osmolyte levels. These observations increase our understanding of the role of NO in drought stress response in Arabidopsis.
Highlights
As a gaseous diatomic radical, nitric oxide (NO) is an essential endogenous signalling molecule involved in multiple physiological processes in plants, including growth, development, and response to environmental stresses (Shi et al, 2012b, c)
The leaf water content (LWC) gradually declined in all plants, but the decline was greater in the WT than in the neuronal NO synthase (nNOS) transgenic plants (Fig. 1a)
Consistent with the decline in LWC, all plants showed a gradual increase in electrolyte leakage (EL) after drought stress treatment, but the increase was less in the nNOS transgenic lines than in the WT (Fig. 1b)
Summary
As a gaseous diatomic radical, nitric oxide (NO) is an essential endogenous signalling molecule involved in multiple physiological processes in plants, including growth, development, and response to environmental stresses (Shi et al, 2012b, c). Further bioinformatics analysis identified several common transcription factorbinding sites (TFBSs) that are enriched in the promoters of these NO-responsive genes, such as WRKY, GBOX, and octopine synthase element-like sequence (OCSE) (Palmieri et al, 2008) Most of these results were obtained by exogenous application of NO donors such as sodium nitroprusside (SNP), S-nitroso-N-acetyl-d-penicillamine (SNAP), and nitrosoglutathione (GSNO), NO scavengers such as 2-[4-carboxyphenyl]-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide (c-PTIO), or mammalian-type NO synthase (NOS) or its inhibitors including l-NG-nitro arginine methylester (l-NAME) (Huang et al, 2002; Polverari et al, 2003; Parani et al, 2004; Grün et al, 2006; Palmieri et al, 2008; Besson-Bard et al, 2009). Recent studies sshowed inconsistent findings concerning the effects of these NOS inhibitors, indicating that these chemicals have different or even opposite metabolic effects, and care must be taken in making inferences based on the use of these NO-modulating compounds (Arasimowicz-Jelonek et al, 2011; Gupta et al, 2011)
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