Protein phosphatase inhibitors activate anti‐fungal defence responses of soybean cotyledons and cell cultures

Abstract

SummaryThe application of a variety of structurally different protein phosphatase inhibitors (okadaic acid, acanthifolicin, microcystins, nodularin, tautomycin, calyculin A, cantharidin and endothall) to cut surfaces of soybean cotyledons (Glycine max L.) resulted in the production of isoflavonoid phytoalexins (plant defence compounds). Daidzein was the predominant isoflavonoid produced by soybean cotyledons in response to protein phosphatase inhibitors. In contrast, several isoflavonoid phytoalexins were seen after application of either an elicitor I~-glucan fraction isolated from yeast extract or hepta-(133, l~6)-~-glucoside which is the most potent elicitor-active component isolated from the soybean pathogen Phytophthora megasperma f. sp. glycinea. Isoflavonoid production in response to either protein phosphatase inhibitors or elicitors reached a maximum after 20-24 h. The addition of protein phosphatase inhibitors to a soybean cell suspension culture induced the expression of phenylalanine ammonia-lyase (PAL), the first enzyme in the isoflavonoid biosynthetic pathway. Induction of PAL activity was blocked by protein synthesis inhibitors, cycloheximide or anisomysin, and largely prevented by a protein kinase inhibitor, K252a. Another common response of plant cells to fungal elicitation, alkalinization of the soybean cell culture media, was induced within minutes in response to protein phosphatase inhibitors and was largely prevented by K252a.

Rapid and Transient Activation of a Myelin Basic Protein Kinase in Tobacco Leaves Treated with Harpin from Erwinia amylovora

“…Protein phosphorylation has been implicated in the initiation of defined defense responses to elicitors in a number of plant-pathogen interactions (Dietrich et al, 1990;Felix et al, 1991;Levine et al, 1994;MacKintosh et al, 1994;Viard et al, 1994). However, much less is known about the specific PKs and/or phosphatases and their regulation, possible interaction, and target(s) in signaling cascade(s).…”

Short-Lived and Phosphorylated Proteins Contribute to Carrier-Mediated Efflux, but Not to Influx, of Auxin in Suspension-Cultured Tobacco Cells1

“…The inhibitors were expected to permeate the PM according to their chemical structure and their ability to elicit rapid defense responses in plant cells (MacKintosh et al, 1994;Mathieu et al, 1996a;Smith and Walker, 1996). (Table III), whereas calyculin A (0.2 m, 30 min) and cantharidin (50 m, 60 min) inhibited the activity of the influx carrier by 16 and 55% (not shown) and that of the efflux carrier by 57 and 77% (Table III).…”

Antifungal activity of tautomycin and related compounds against Sclerotinia sclerotiorum

“…Tautomycin is a good inhibitor of PPs. 4,[6][7][8] From the Kawamura et al's study 19 of different moieties of tautomycin involved in the inhibition of PP, they suggest that the C22-C26 moiety is essential for inhibition of PP and the anhydride moiety enhances the inhibition. Although the PP was inhibited by tautomycin, whether the inhibition of tautomycin causes the antifungal activity needs further work to verify.…”

“…Tautomycin significantly inhibits microbial growth (MIC¼6.52Â10 À4 mM), has strong antifungal activity against S. sclerotiorum, and inhibits types 1 and 2A of protein phosphatase (PP) activity. [4][5][6][7][8][9] Potent biological activities of tautomycin has stimulated other research groups to investigate its biosynthesis 10 and chemical synthesis. 11 However, it was not commercially produced as the fungicide against S. sclerotiorum because of its high toxicity to mice (LD 50 ¼7.5 mg kg À1 , orally).…”