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The plant aspartate aminotransferase gene family
Author(s) -
Wadsworth Gregory J.
Publication year - 1997
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1997.tb00028.x
Subject(s) - isozyme , plastid , biology , complementary dna , cytosol , gene , subcellular localization , peroxisome , nuclear gene , biochemistry , mitochondrion , organelle , glyoxysome , genetics , medicago truncatula , genome , microbiology and biotechnology , enzyme , chloroplast , symbiosis , bacteria
Aspartate aminotransferase exists as multiple isozymes in plants. These AAT isozymes are differentially localized in at least four different subcellular compartments, including the cytosol, plastids, mitochondria, and peroxisomes. The recent characterization of cDNA and genomic sequences encoding AAT from several plants has provided insight into the structure, subcellular targeting, and evolution of the AAT isozymes. The AAT isozymes appear to be targeted to subcellular compartments by the same mechanisms utilized by other targeted proteins. Both the plastid AAT and mitochondrial AAT are synthesized as precursors with appropriate N‐terminal targeting sequences which are proteolytically removed after localization in their respective organelles. The cytosolic AAT isozymes lack apparent targeting sequences, thus restricting it to the cytosol. A peroxisomal AAT has not been cloned and therefore its targeting has not been investigated. Sequence analysis demonstrates that the plant AAT isozymes are in the same protein family as the vertebrate and bacterial AATs. Furthermore, similarity between vertebrate and plant mitochondrial AAT isozymes suggest the evolution of this AAT isozyme may predate the divergence of plants and animals. Analysis of plastid and cytosolic AAT suggests that they have diverged more recently than the mitochondrial gene. The sequence analysis also reveals that the cytosolic AAT is diverging at a rate 1.6 times faster than the plastid AAT. The cDNA and genomic clones have been used to investigate expression of the AAT genes during nodulation in legumes and suggest that the nodule‐enhanced expression of plastid AAT is controlled at the transcriptional level.