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Yeast 5‐aminolevulinate synthase provides additional chlorophyll precursor in transgenic tobacco
Author(s) -
Zavgorodnyaya Anna,
Papenbrock Jutta,
Grimm Bernhard
Publication year - 1997
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1997.12010169.x
Subject(s) - tetrapyrrole , biochemistry , plastid , biology , chloroplast , transgene , chlorophyll , chloroplast stroma , enzyme , gene , thylakoid , botany
Summary Synthesis of the tetrapyrrole precursor 5‐aminolevulinate (ALA) in plants starts with glutamate and is a tRNA‐dependent pathway consisting of three enzymatic steps localized in plastids. In animals and yeast, ALA is formed in a single step from succinyl CoA and glycine by aminolevulinate synthase (ALA‐S) in mitochondria. A gene encoding a fusion protein of yeast ALA‐S with an amino‐terminal transit sequence for the small subunit of ribulose bisphosphate carboxylase was introduced into the genome of wild‐type tobacco and a chlorophyll‐deficient transgenic line expressing glutamate 1‐semi‐aldehyde aminotransferase (GSA‐AT) antisense RNA. Expression of ALA‐S in the GSA‐AT antisense transgenic line provided green‐pigmented co‐transformants similar to wild‐type in chlorophyll content, while transformants derived from wild‐type plants did not show phenotypical changes. The capacity to synthesize ALA and chlorophyll was increased in transformed plants, indicating a contribution of ALA‐S to the ALA supply for chlorophyll synthesis. ALA‐S activity was detected in plastids of the transformants. Preliminary evidence is presented that succinyl CoA, the substrate for ALA‐S, can be synthesized and metabolized in plastids. The transgenic plants formed chlorophyll in the presence of gabaculine, an inhibitor of GSA‐AT. Steady‐state RNA and protein levels and, consequently, the enzyme activity of GSA‐AT were reduced in plants expressing ALA‐S. In analogy to the light‐dependent ALA synthesis attributed to feedback regulation, a mechanism at the level of intermediates or tetrapyrrole end‐products is proposed, which co‐ordinates the need for heme and chlorophyll precursors and restricts synthesis of ALA by regulating GSA‐AT gene expression. The genetically engineered tobacco plants containing the yeast ALA‐S activity demonstrate functional complementation of the catalytic activity of the plant ALA‐synthesizing pathway and open strategies for producing tolerance against inhibitors of the C5 pathway.