Jeremy N. Friedberg* Eva Czarnecka-Verner, Suzanne Cunningham, Steve R. Bowley and Bryan McKersie.

University of Guelph, Department of Plant Agriculture, Plant Biotechnology Division, Guelph, ON, Canada.

Plants respond to heat shock and many other environmental stresses, by increasing the presence of several families of proteins referred to as heat shock proteins (HSPs). A family of nuclear-encoded trans-acting transcription factors, termed the heat shock factor (HSF), governs the expression of HSPs. Nine different HSF genes have been identified that have considerable sequence and functional homology across species. To study HSF expression in alfalfa (Medicago sativa), a probe generated from an Arabidopsis HSF sequence (AtHSF21) was employed to screen a cDNA library (provided by S Cunningham and J Volenec, Purdue University). The library was constructed in lambda ZAP vectors using alfalfa (cultivar Norseman) mRNA isolated from crown buds of cold acclimated plants. Sequencing of positive clones revealed a new alfalfa HSF homologue that possesses high homology to Nicotiana tabacum HSF2 and Arabidopsis thaliana HSF21. Further sequence and structural homology analysis indicated that the new alfalfa HSF homologue (designated MsHSFA4-6, accession number AF235958) belongs to the class A4 HSFs. Members of this family are activators of heat shock genes and are typically induced in response to heat stress. To confirm its activity, alfalfa total RNA was isolated from tissue treated at 40C for 1 hour. Northern and slot blot analysis revealed that MsHSF6 transcripts are induced in response to heat stress, confirming its activity and its designation as a class A4 HSF. MsHSF6 expression during acclimation and various stress conditions is described.

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