Understanding the regulation of proline content in source leaves of winter oilseed rape by using transcriptomic and 15N-isotope tracing approaches

IntroductionProline metabolism is an essential component of plant adaptation to multiple environmental stress conditions that is also known to participate in specific developmental phases, particularly in reproductive organs [1,2]. Recent evidences suggested a possible role for proline catabolism in B. napus for nitrogen remobilization processes during sink to source transition at the vegetative stage [3,4,5].Technological and methodological innovation Here, we analyzed the transcriptional regulation of the P5CS/ProDH balance at the vegetative stage during sink to source transition with respect to net proline biosynthesis and degradation fluxes. To do so, we performed 15N labelling experiment with either 15NH4 or 15N-proline during 4 hours and monitored the redistribution of 15N towards amino acids by taking advantage of an UPLC-TQD analytical system. Results and impactWe showed that the downregulation of three P5CS1 genes during sink to source progression was accompanied by a reduced commitment of de novo assimilated 15N towards proline biosynthesis and an overall depletion of free proline content. Inversely, the regulation of ProDH transcript levels during sink to source transition was not correlated with the evolution of the maximal degradation capacity for proline. Our results suggest a role for proline catabolism in B. napus at a late stage of senescence