The Arabidopsis N-acetylornithine deacetylase controls ornithine biosynthesis via a linear pathway with downstream effects on polyamine levels.

Arabidopsis thaliana At4g17830 codes for a protein showing sequence similarity with the Escherichia coli N-acetylornithine deacetylase (EcArgE), an enzyme implicated in the linear ornithine (Orn) biosynthetic pathway. In plants, N-acetylornithine deacetylase (NAOD) activity has yet to be demonstrated; however, At4g17830-silenced and mutant (atnaod) plants display an impaired reproductive phenotype and altered foliar levels of Orn and polyamines (PAs). Here, we showed the direct connection between At4g17830 function and Orn biosynthesis, giving the biochemical demonstration that At4g17830 codes for a NAOD. These results are the first experimental proof that Orn can be produced in Arabidopsis via a linear pathway. In this study, to identify the role of AtNAOD in reproductive organs, we carried out a transcriptomic analysis on atnaod mutant and wild-type flowers. In the atnaod mutant, the most relevant effects were the reduced expression of cysteine-rich peptide–coding genes, known to regulate male–female crosstalk during reproduction, and variation in the expression of genes involved in nitrogen:carbon (N:C) status. The atnaod mutant also exhibited increased levels of sucrose and altered sensitivity to glucose. We hypothesise that AtNAOD participates in Orn and PA homeostasis, contributing to maintain an optimal N:C balance during reproductive development. atnaod mutant and wild-type plants fertilised flowers (stage 15) were compared. Three independent biological replicates were conducted for both atnaod mutant and wild-type plants. Each biological sample consists of approximately 100 harvested fertilised flowers collected from a population of 17-20 plants.