ESTs reveal a multigene family for plant defensins inArabidopsis thaliana

Abstract

Plant defensins, formerly named γ-thionins, are a group of small, cysteine-rich, basic, and antimicrobial plant proteins. Random sequencing of expressed sequence tags (ESTs) in Arabidopsis thaliana has revealed several different plant defensin genes in this plant species which can be grouped into two subfamilies. We have used one EST of each subfamily to study the expression of the corresponding genes in A. thaliana. Pdfl.3 is constitutively expressed in seedlings, rosettes, flowers, and siliques and is not inducible in seedlings either by methyl jasmonate, salicylate, ethephon, and silver nitrate or by several different phytopathogenic fungi. The expression of a second gene, Pdfl.2, is in untreated plants only detectable in rosettes. In seedlings, it is inducible by methyl jasmonate, silver nitrate, and different phytopathogenic fungi, notably Fusarium oxysporum f. sp. matthiolae. The regulation of Pdfl.2 resembles that of the pathogen-inducible thionin gene TM2.1.

Overexpression of an endogenous thionin enhances resistance of Arabidopsis against Fusarium oxysporum.

“…The same results have been obtained for the Pdfl.2 gene (Epple et al, 1997). It is therefore possible that the systemic protection of Arabidopsis and also of radish by biocontrol bacteria uses the salicylate-independent pathway that induces the 7/7/2.1 and Pdf1.2 genes, leading to the accumulation of THI2.1 and PDF1.2 antimicrobial proteins.…”

“…Plant defensins have in vitro antimicrobial activity (e.g., Terras et al, 1995), and we predict that coexpression of the induced plant defensin with THI2.1 will result in higher protection against F. o. matthiolae. Transcripts for Pdf1.2 are highly induced by F. o. matthiolae as are Thi2.1 transcripts, and both genes are probably regulated by the same signal transduction pathway (Epple et al, 1997). The toxic mechanisms by which thionins and plant defensins exert their antimicrobial activity are different (Thevissen et al, 1996), and both THI2.1 and PDF1.2 might display a synergistic effect as has been found for hordothionin and other cysteine-rich proteins in vitro (Molina et al, 1993;Terras et al, 1993).…”

“…These include PR-1 and PR-5 as well as the plant defensin gene Pdf1.2 (Figure 8; Epple et al, 1997). The products of these and perhaps other still unknown defense genes might act together with THI2.1.…”

Arabidopsis SON1 Is an F-Box Protein That Regulates a Novel Induced Defense Response Independent of Both Salicylic Acid and Systemic Acquired Resistance

“…We identified five son ( suppressor of nim1-1 ) mutants based on their pathogen-resistant phenotype. One of these, son1 , exhibited heightened resistance without the attendant induction of SAR-associated PR genes or PDF1.2 , a marker for a jasmonic acid-dependent inducible defense response (Epple et al, 1997;Manners et al, 1998). Resistance in son1 also was expressed in the presence of nahG , indicating that it does not require SA accumulation.…”

Protective effect of an antimicrobial peptide from Mytilus edulis chilensis expressed in Nicotiana tabacum L.

“…In plants, genes encoding defensins are developmentally regulated, with a predominant expression in outer cell layers (Moreno et al 1994;Terras et al 1995), and can be induced above basal levels in response to pathogen infection and other stresses (Chiang and Hadwiger, 1991;Moreno et al 1994;Terras et al 1995;Penninckx et al 1996;Epple et al 1997). Additionally, certain defensin genes are down-regulated by some pathogens (Moreno et al 1994).…”