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Summary.To determine whether the expression of cell wall related genes changes during the establishment of an arbuscular mycorrhizal symbiosis (AM), we studied the expression of a maize hydroxyproline-rich glycoprotein (HRGP) gene. In situ hybridization showed that, in differentiated ceils of maize roots, mRNA accumulation corresponding to the gene encoding for HRGP was only found when the cells were colonized by the endomycorrhizal fungus Glomus versiforme.

Rat liver nuclear extracts were tested for the presence of factors which might be common to the transcriptional regulation of both the albumin and a-foetoprotein genes. Gel shift assay showed the formation of three complexes (I, I1 and 111) with the albumin probe. Two of them (I and 111) could be displaced by the a-foetoprotein promoter. Analysis of nuclear extracts from liver, kidney, spleen and brain and competition experiments using several oligonucleotides covering regions from the albumin and a-foetoprotein promoters showed that complex 111 results from the binding of the ubiquitous nuclear factor 1, while complex I1 involves a CCAAT-box-binding protein also detected in brain and spleen extracts. Complex I is formed upon binding of a liver-specific factor to a proximal element of the rat albumin promoter. This factor also binds to a similar sequence in the a-foetoprotein promoter and is closely related to the hepatocyte nuclear factor 1, as shown by competition experiments using an oligonucleotide covering its target sequence on the p-fibrinogen promoter.Transfection competition experiments indicated that, in vivo, this factor acts as a positive trans-acting element in the expression of both the rat albumin and a-foetoprotein genes.The albumin -a-foetoprotein gene system is a powerful model for gaining insight into the mechanisms which regulate the tissue-and stage-specific transcription of eucaryotic genes. The two genes, which belong to the same family [I], are both transcribed in the liver in a reciprocal manner during the course of development [2, 31. a-Foetoprotein gene transcription is high during fetal life and gradually shuts off after birth to reach almost undetectable levels during normal adult life, while the transcription of albumin gene reaches a maximum after the fetal stage and remains high throughout adult life.Considerable information has recently been obtained on the molecular mechanisms governing the expression of the albumin and a-foetoprotein genes in the liver (see [4] for review). In particular, transient expression experiments indicated that their promoter regions are involved in the specificity of expression of these genes in the liver of several species [5 -121. As this specificity of expression is probably confered by the binding of trans-acting factors to regulatory DNA regions (see [13 -151 for reviews), the identification of nuclear factors interacting with these promoters is of fundamental importance. The albumin promoter region has recently been shown to bind several proteins [16-181. Our recent study of the binding of nuclear proteins to the rat a-foetoprotein promoter indicated that a liver-specific factor and nuclear factor 1 can recognize two elements of the a-foetoprotein promoter [19]. We have now compared the binding of rat liver nuclear pro- teins to the rat albumin and a-foetoprotein promoters in order to detect common factors which may be involved in the transcriptional regulation of these genes. Such proteins may have a more general role in controlling the liver-sp...