Pyrroline-5-carboxylate dehydrogenase is a key actor of nitrogen metabolism in maturing seeds of Arabidopsis thaliana

Abstract Proline is a multifaceted amino acid in plants involved in both stress responses and development. Recent studies have shown that knock-out mutants lacking Pyrroline-5-carboxylate dehydrogenase (P5CDH), the enzyme responsible for the second step of proline catabolism, impaired nitrogen remobilisation and carbon allocation to seeds. Here, we demonstrate that seed development is also significantly impaired in p5cdh mutants, particularly from the transition between embryogenesis and maturation. Specifically, the p5cdh mutation leads to an arrest in embryo elongation and a reprogramming of seed metabolism during maturation, resulting in reduced accumulation of storage compounds and compromised acquisition of dehydration tolerance. These effects are further exacerbated under high nitrate conditions. Together, our findings highlight a crucial role for proline catabolism in supporting the ability of maturing embryos to utilize glutamine as a nitrogen source, particularly in response to nitrogen availability.