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| Title: Characterization of rice anthranilate synthase alpha-subunit genes OASA1 and OASA2 .
Tryptophan accumulation in transgenic rice expressing a feedback-insensitive mutant of OASA1 .
| | Author: Tozawa Y Hasegawa H Terakawa T Wakasa K | | Journal: Plant Physiol .
Citation: V : 126 ( 4 ) P : 1493-506 Year: 2001 Type: ARTICLE | | Literature: oryza Field: abstract Doc ID: pub11500548 Accession (PMID): 11500548 | | Abstract: Anthranilate synthase ( AS ) is a key enzyme in the synthesis of tryptophan ( Trp ) , indole-3-acetic acid , and indole alkaloids .
Two genes , OASA1 and OASA2 , encoding AS alpha-subunits were isolated from a monocotyledonous plant , rice ( Oryza sativa cv Nipponbare ) , and were characterized .
A phylogenetic tree of AS alpha-subunits from various species revealed a close evolutionary relationship among OASA1 and Arabidopsis ASA2 , Ruta graveolens AS alpha 2 , and tobacco ASA2 , whereas OASA2 , Arabidopsis ASA1 , and R graveolens AS alpha 1 were more distantly related .
OASA1 is expressed in all it issues tested , but the amount of its mRNA was greater in panicles than in leaves and roots .
The abundance of OASA2 transcripts is similar among it issues and greater than that of OASA1 transcripts ; furthermore , OASA2 expression was induced by a chitin heptamer , a potent elicitor , suggesting that OASA2 participates in secondary metabolism .
Expression of wild-type OASA1 or OASA2 transgenes did not affect the Trp content of rice calli or plants .
However , transformed calli and plants expressing a mutated OASA1 gene , OASA1 ( D323N ) , that encodes a protein in which aspartate-323 is replaced with asparagine manifested up to 180 and 35-fold increases , respectively , in Trp accumulation .
These transgenic calli and plants were resistant to 300 microM 5-methyl-Trp , and AS activity of the calli showed a markedly reduced sensitivity to Trp .
These results show that OASA1 is important in the regulation of free Trp concentration , and that mutation of OASA1 to render the encoded protein insensitive to feedback inhibition results in accumulation of Trp at high levels .
The OASA1 ( D323N ) transgene may prove useful for the generation of crops with an increased Trp content . | Matching Sentences:
[ Sen. 3, subscore: 1.00 ]: A phylogenetic tree of AS alpha-subunits from various species revealed a close evolutionary relationship among OASA1 and Arabidopsis ASA2 , Ruta graveolens AS alpha 2 , and tobacco ASA2 , whereas OASA2 , Arabidopsis ASA1 , and R graveolens AS alpha 1 were more distantly related .
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