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

Arabidopsis p5cdhmutants have defects in stem-to-seed resource allocation and reveal a key role of pyrroline-5-carboxylate dehydrogenase in carbon and nitrogen remobilization for seed filling. Proline is an amino acid that is degraded in the mitochondria by the sequential action of proline dehydrogenase (ProDH) and pyrroline-5-carboxylate dehydrogenase (P5CDH) to form glutamate. We investigated the phenotypes of Arabidopsis wild-type plants, the knockout prodh1 prodh2 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. Analyses of elements in above-ground organs revealed lower C concentrations in the p5cdh seeds. Determination of C, N, and dry matter partitioning among the above-ground organs revealed a major defect in stem-to-seed resource allocations in this mutant. Again surprisingly, defects in C, N, and biomass allocation to seeds dramatically increased in high-N conditions. N-15-labelling consistently confirmed the defect in N remobilization from the rosette and stem to seeds in p5cdh. Consequently, the p5cdh mutants produced morphologically abnormal, C-depleted seeds that displayed very low germination rates. The most striking result was the strong amplification of the N-remobilization defects in p5cdh under high nitrate supply, and interestingly this phenotype was not observed in the prodh1 prodh2 double-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.

Automated summary

This study investigated the phenotypes of Arabidopsis plants with mutations in the p5cdh gene and found that these mutants had lower seed yield and produced lighter seeds, indicating defects in stem-to-seed resource allocation. Furthermore, under high nitrate supply, the defects in carbon, nitrogen, and biomass allocation to seeds in p5cdh mutants were significantly amplified. Interestingly, these defects were not observed in the prodh1 prodh2 double-mutant. This study highlights the essential role of P5CDH in the carbon and nitrogen remobilization for seed development in Arabidopsis.