The saccharopine pathway in seed development and stress response of maize

• Published in: Plant, cell and environment cell and environment, 2015-11, Vol.38 (11), p.2450-2461
• Main Authors: Kiyota, Eduardo, Pena, Izabella Agostinho, Arruda, Paulo
• Format: Article
• Language: English
• Subjects: Aldehydes - metabolism; Amino acids; Carbon dioxide; Corn; Dehydrogenase; Hybridization, Genetic; Kinetics; Leaves; Lysine - metabolism; lysine catabolism; Metabolic Networks and Pathways; Metabolites; Models, Biological; osmotic stress; pipecolic acid; Plant tissues; Saccharopine Dehydrogenases - metabolism; Seeds - genetics; Seeds - growth & development; Seeds - metabolism; transcription regulation; Wheat; Zea mays - genetics; Zea mays - growth & development; Zea mays - metabolism
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.12563

Lysine is catabolized in developing plant tissues through the saccharopine pathway. In this pathway, lysine is converted into α‐aminoadipic semialdehyde (AASA) by the bifunctional enzyme lysine‐ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH). AASA is then converted into aminoadipic acid (AAA) by aminoadipic semialdehyde dehydrogenase (AASADH). Here, we show that LKR/SDH and AASADH are co‐expressed in the sub‐aleurone cell layers of the developing endosperm; however, although AASADH protein is produced in reproductive and vegetative tissues, the LKR/SDH protein is detectable only in the developing endosperm. AASADH showed an optimum pH of 7.4 and Kms for AASA and NAD+ in the micromolar range. In the developing endosperm, the saccharopine pathway is induced by exogenous lysine and repressed by salt stress, whereas proline and pipecolic acid synthesis are significantly repressed by lysine. In young coleoptiles, the LKR/SDH and AASADH transcriptions are induced by abiotic stress, but while the AASADH protein accumulates in the stressed tissues, the LKR/SDH protein is not produced. In the developing seeds, the saccharopine pathway is used for pipecolic acid synthesis although proline may play a major role in abiotic stress response. The results indicate that the saccharopine pathway in maize seed development and stress responses significantly differ from that observed for dicot plants. Although ear emergence strongly alters C/N partitioning in wheat, phenology driven modifications in leaf in proteomic profile, metabolite content and nutrition of wheat exposed to elevated [CO2] remain to be elucidated. Our study revealed that, compared with vegetative stage, growth at elevated CO2 altered photosynthate export and tended to accelerate leaf N remobilization during grain filling period. Protein derived N remobilization modulated leaf proteins and amino acids profile. Finally our study highlighted the fact that under elevated [CO2] nitrogen use efficiency improvement might represent a target goal for breeding programmes.