Early Biosynthetic Pathway to Abscisic Acid inCercospora cruenta

Abstract

A new biosynthetic intermediate of ABA, (2Z,4E)-gamma-ionylideneacetaldehyde, was isolated from young mycelia of Cercospora cruenta. Under an (18)O2 atmosphere, an oxygen atom of this endogenous aldehyde was exclusively labeled. Similarly, three (18)O atoms were incorporated into the ABA molecule recovered after prolonged incubation; selectively labeled were one of the carboxyl oxygen atoms and the two on the ring portion of ABA. A feeding experiment with [1-(13)C]glucose proved the exclusive operation of the mevalonate pathway for the formation of both ABA and beta-carotene. These results suggest that (2Z,4E)-gamma-ionylideneacetaldehyde can be a key ABA biosynthetic intermediate formed by the oxidative cleavage of a carotenoid precursor.

Biosynthesis of Abscisic Acid by the Direct PathwayviaIonylideneethane in a Fungus,Cercospora cruenta

“…The result of 18 O-labeling of ABA was different from that reported by Yamamoto et al 8) This difference can be explained by the metabolic rate of 6 to ABA. Accumulation of compound 6 in their cultural condition suggests slow turnover of 6 to ABA.…”

“…The phytopathogenic fungi Cercospora cruenta, IFO6134, which was used by Yamamoto et al, 8) Isolation of 4. After culture of C. cruenta for 7 d in an 18 O 2 atmosphere, the mycelia were recovered and washed with 30 ml of distilled water.…”

“…7,14) The production of these compounds appears to support the direct pathway, but the fungus produces -carotene and an aldehyde-intermediate, 2Z,4E--ionylideneacetaldehyde (6), and incorporates 18 O from 18 O 2 into C-1, -1 0 , and -4 0 of ABA. 8) These facts suggest that ABA of the fungus is biosynthesized by the carotenoid pathway, although the 9Z-carotenoid possessing -ring that should be a precursor of 6 has not been found in this fungus. We re-examined the 18 O-labeling of ABA with 18 O 2 , made precise analysis of ABA-related carotenoids and sesquiterpenoids, and did feeding experiments of labeled compounds in C. cruenta to solve the confusion over the biosynthesis of ABA.…”

“…1, and the carotenoid pathway might be similar to that of plant ABA. 8) Sufficient evidence appears to be lacking for these two pathways, since the intermediates between FDP and ionylideneethanol have not been found for the direct pathway, [9][10][11] and the immediate precursor carotenoids have not been found for the carotenoid pathway. We found that a phytopathogenic fungus, Botrytis cinerea, biosynthesized ABA by the direct pathway via ionylideneethane.…”

The P450 Monooxygenase BcABA1 Is Essential for Abscisic Acid Biosynthesis in Botrytis cinerea

“…Biochemical analyses in various Cercospora species provide evidence that these fungi synthesize ABA directly from farnesyl diphosphate, via different oxidative steps, with either 1Ј-4Ј-dihydroxy-␥-ionylidene acetate, 1Ј-deoxy-ABA, or 1Ј-4Ј-trans-diol ABA as intermediates, and not via the carotenoid pathway used by higher plants (1,(20)(21)(22). However, the presence of the carotenoid pathway in fungi cannot be excluded (40). In B. cinerea, biosynthesis of ABA seems to follow a pathway which is similar to the major route in Cercospora pini-densiflorae, i.e., via 1Ј-4Ј-trans-diol-ABA (13).…”