Search

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. 15N-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 prodh 2 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. [ABSTRACT FROM AUTHOR]

Leaf senescence is a form of developmentally programmed cell death that allows the remobilization of nutrients and cellular materials from leaves to sink tissues and organs. Among the catabolic reactions that occur upon senescence, little is known about the role of proline catabolism. In this study, the involvement in dark-induced senescence of proline dehydrogenases (ProDHs), which catalyse the first and rate-limiting step of proline oxidation in mitochondria, was investigated using prodh single- and double-mutants with the help of biochemical, proteomic, and metabolomic approaches. The presence of ProDH2 in mitochondria was confirmed by mass spectrometry and immunogold labelling in dark-induced leaves of Arabidopsis. The prodh1 prodh2 mutant exhibited enhanced levels of most tricarboxylic acid cycle intermediates and free amino acids, demonstrating a role of ProDH in mitochondrial metabolism. We also found evidence of the involvement and the importance of ProDH in respiration, with proline as an alternative substrate, and in remobilization of proline during senescence to generate glutamate and energy that can then be exported to sink tissues and organs. [ABSTRACT FROM AUTHOR]