Kiyota Eduardo, Pena Izabella Agostinho, Arruda Paulo
Centro de Biologia Molecular e Engenharia Genética, Universidade Estadual de Campinas, 13083-875, Campinas, Sao Paulo, Brazil.
Departamento de Genética e Evolução, Instituto de Biologia, Universidade Estadual de Campinas, 13083-875, Campinas, Sao Paulo, Brazil.
Plant Cell Environ. 2015 Nov;38(11):2450-61. doi: 10.1111/pce.12563. Epub 2015 Jul 16.
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.
在发育中的植物组织中，赖氨酸通过酵母氨酸途径进行分解代谢。在该途径中，赖氨酸由双功能酶赖氨酸 - 酮戊二酸还原酶/酵母氨酸脱氢酶（LKR/SDH）转化为α - 氨基己二酸半醛（AASA）。然后，AASA由氨基己二酸半醛脱氢酶（AASADH）转化为氨基己二酸（AAA）。在此，我们表明LKR/SDH和AASADH在发育中的胚乳亚糊粉细胞层中共表达；然而，尽管AASADH蛋白在生殖和营养组织中产生，但LKR/SDH蛋白仅在发育中的胚乳中可检测到。AASADH的最适pH为7.4，对AASA和NAD(+)的Km值在微摩尔范围内。在发育中的胚乳中，酵母氨酸途径受外源赖氨酸诱导，受盐胁迫抑制，而脯氨酸和哌啶酸的合成则受赖氨酸显著抑制。在幼嫩的胚芽鞘中，LKR/SDH和AASADH的转录受非生物胁迫诱导，但虽然AASADH蛋白在受胁迫组织中积累，但LKR/SDH蛋白未产生。在发育中的种子中，酵母氨酸途径用于哌啶酸的合成，尽管脯氨酸可能在非生物胁迫响应中起主要作用。结果表明，玉米种子发育和胁迫响应中的酵母氨酸途径与双子叶植物中观察到的途径显著不同。
