Abstract

To overcome stresses such as osmotic shock and pathogen attack, internal signals activate plant defense responses. The F8A24.12 gene from Arabidopsis thaliana encodes the serine/threonine protein kinase with the highest similarity at the structural and functional level to a salt-stress induced gene, Esi47 , from the salt tolerant wheatgrass Lophopyrum elongatum . Both genes have a small upstream open reading frame (suORF) in their 5 ' untranslated region (5 ' UTR). This element was previously shown to have a regulatory function in the Esi47 gene. Northern blot analysis revealed that under salt stress both genes have an increased level of transcription. Transgenic Arabidopsis plants were produced carrying reporter gene encoding the enzyme Ý-glucuronidase (GUS) under the control of the F8A24.12 promoter and 5 ' UTR. GUS histochemical assays revealed that F8A24.12 gene expression occurs throughout the life of the plant, particularly in the root elongation zone, in the vascular tissues of roots and leaves, in the flower and in the petal and sepal abscission zone. GUS fluorometric assays demonstrated that the quantity of GUS protein is induced by methyl jasmonate (MeJA) treatment after 12, 24 and 36 hrs and by salt stress after 24 hrs treatment. These data suggest that the F8A24.12 gene is part of the jasmonic acid signaling pathway. This phytohormone is related to the plant growth and plant defense responses. GUS fluorometric assays were also performed on transgenic Arabidopsis carrying an altered suORF promoter-GUS fusion. Mutation of the suORF obliterated the MeJA and salt responsiveness of the F8A24.12 gene promoter plus 5 ' UTR transgene.