Molecular insights on the role of Arabidopsis thaliana NAOD in fruit set

Ornithine (Orn), an intermediate of arginine and polyamines (PAs) biosynthetic pathways, is produced in plants by N2-acetylornithine:Nacetylglutamate acetyltransferase (NAOGAcT). In enteric bacteria, Orn is synthesised also by N-acetylornithine deacetylase (NAOD) via a linear pathway. The plants seem to be unable to use this pathway despite the presence of many NAOD-like genes identified in various plant species. We have studied the role of the putative NAOD of Arabidopsis (At4g17830) by analysing the effects of its downregulation in vivo. AtNAOD-suppressed plants displayed an impaired fruit setting. AtNAOD downregulation determined a reduced Orn content and altered PAs levels. To elucidate the role of AtNAOD in fruit setting, we compared the mRNA profile of fertilised flowers of AtNAOD-downregulated plants with that of wild-type. We found 63 genes significantly changed (fold change ≥ |2|). Our analysis revealed that the altered Orn and PAs metabolism in the reproductive organs of the AtNAOD-downregulated plants is associated with an impaired transcription of cysteine-rich signalling peptides involved in male-female cross-talk and perturbation of genes involved in regulating N:C status.