Carbon and nitrogen remobilization during seed filling is strongly impaired in pyrroline-5-carboxylate dehydrogenase mutant


 Proline is an amino acid which is degraded in the mitochondrion by the sequential action of Proline Dehydrogenase (ProDH) and Pyrroline-5-Carboxylate Dehydrogenase (P5CDH) to form glutamate. We investigated the phenotypes of Arabidopsis wildtype plants, knockout prodh1prodh2 double mutant and knockout p5cdh allelic mutants grown at low and high nitrate supplies. Surprisingly, only p5cdh presented lower seed yield and produced lighter seeds. Elementary analyses in above ground organs revealed lower C concentrations in the p5cdh seeds. The computing of C, N, and dry matter partitioning between the above ground organs revealed a major defect in stem to seed resource allocations in p5cdh. Surprisingly defects in C, N and biomass allocation to seeds dramatically increased in high N conditions. 15N-labbeling consistently confirmed the defect of N remobilization from rosette and stem to seeds in p5cdh. Consequently, p5cdh mutants produced morphologically abnormal C-depleted seeds that displayed very low germination rates. The most striking result is the strong amplification of the N remobilization defects in p5cdh by high nitrate supply. Interestingly, such phenotype was not observed in prodh1prodh2 mutant irrespective of nitrate supply. This study reveals an essential role of p5cdh in carbon and nitrogen remobilization for reserve accumulation during seed development in Arabidopsis.