Revealing the function of the plastidial serine biosynthesis pathway in Arabidopsis thaliana

植物有几种合成丝氨酸的可能性。最突出的途径是光呼吸途径，这被认为是光合作用细胞合成丝氨酸的主要途径。在非光合作用细胞中，丝氨酸可能通过磷酸丝氨酸途径(PS途径)合成。然而，这一途径在植物中的功能还远未被了解。我们的初步结果表明，PS途径中的一些酶参与色氨酸的合成，而其他酶可能参与衰老过程中氨基酸的降解。此外，我们有强烈的迹象表明，PS途径对于正常的胚胎发育是必不可少的，并在植物发育的后期具有重要的功能。我们的工作旨在揭示这一途径在植物中的作用，特别是发现3-磷酸甘油脱氢酶(PGHD)和磷酸丝氨酸-氨基转移酶(PSAT)不同同工酶的非冗余功能。此外，PGDH酶催化PS途径中的限速步骤，并且已知在其他生物体中受丝氨酸的反馈调节，如大肠杆菌。我们的工作将进一步致力于这种反馈调节在植物中的作用，因此，将确定PGDHs的动力学性质，并将产生PGDH酶的丝氨酸不敏感变体。

Plants have several possibilities for the synthesis of serine. The most prominent pathway is the photorespiration pathway, which is thought to be the major route for serine synthesis in photosynthetic cells. In non-photosynthetic cells serine might be synthesized by the phosphoserine pathway (PS-pathway). However, the function of this pathway in plants is far from being understood. Our preliminary results indicate that some enzymes of the PS-pathway are involved in the synthesis of tryptophan, whereas others might be involved in amino acid degradation during senescence. Furthermore, we have strong indication that the PS-pathway is essential for proper embryo development and have important functions at later stages of plant development. Our work aim at unraveling the role of this pathway in plants, especially to discover the non-redundant function of the different isoenzymes for the 3-phosphoglycerate dehydrogenase (PGHD) and phosphoserine-aminotransferase (PSAT). Additionally, the PGDH enzyme catalyses the rate limiting step within the PS-pathway and is known to be feedback regulated by serine in other organism like Escherichia coli. Our work will further aim on the role of this feedback regulation in plants and therefore, the kinetic properties of the PGDHs will be determined and serine insensitive variants of the PGDH enzyme will be generated.