Evidence for an arginine-dependent route for the synthesis of NO in the model filamentous fungus Aspergillus nidulans.

Antonio Franco‐Cano,Joseph Strauss,Ana T Marcos,David Cánovas

doi:10.1111/1462-2920.15733

Abstract

Nitric oxide (NO) is a signalling molecule in eukaryotic and prokaryotic organisms. NO levels transiently boost upon induction of conidiation in Aspergillus nidulans. Only one pathway for NO synthesis involving nitrate reductase has been reported in filamentous fungi so far, but this does not satisfy all the NO produced in fungal cells. Here we provide evidence for at least one additional biosynthetic pathway in A. nidulans involving l-arginine or an intermediate metabolite as a substrate. Under certain growth conditions, the addition of l-arginine to liquid media elicited a burst of NO that was not dependent on any of the urea cycle genes. The NO levels were controlled by the metabolically available arginine, which was regulated by mobilization from the vacuoles and during development. In vitro assays with protein extracts and amino acid profiling strongly suggested the existence of an arginine-dependent NO pathway analogous to the mammalian NO synthase. Addition of polyamines induced NO synthesis, and mutations in the polyamine synthesis genes puA and spdA reduced the production of NO. In conclusion, here we report an additional pathway for the synthesis of NO in A. nidulans using urea cycle intermediates.

Highlights

Nitric oxide (NO), an abundant short-lived radical, is a signalling molecule in all organisms from bacteria to mammals
We and others observed that NO homeostasis regulates the balance between asexual and sexual reproduction (Maier et al, 2001; Marcos et al, 2016; Marcos et al, 2020; Zhao et al, 2021)
We found that a transient increase of NO is associated with the onset of conidiation and that arginine produces a higher NO level compared to other nitrogen sources such as nitrate

Summary

Introduction

Nitric oxide (NO), an abundant short-lived radical, is a signalling molecule in all organisms from bacteria to mammals. Its signalling role has been extensively studied in mammals, in which it regulates many biological processes such as smooth muscle tone, platelet aggregation and adhesion, cell growth, apoptosis, neurotransmission, vasoconstriction, the reproductive system and sexual behaviour (Rosselli et al, 1998). In plants it regulates growth, development, photoperiod and flowering (He et al, 2004; Kwon et al, 2012). There is a cross-talk between light and NO to regulate the balance between asexual and sexual reproduction (Marcos et al, 2020)

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Discussion

Conclusion