ESTs reveal a multigene family for plant defensins in Arabidopsis thaliana.

Plant defensins, formerly named gamma-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. Pdf2.3 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, Pdf1.2, 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 Pdf1.2 resembles that of the pathogen-inducible thionin gene Thi2.1.