Characterization of expressed meiotic prophase repeat transcript clones of Lilium: meiosis-specific expression, relatedness, and affinities to small heat shock protein genes

Abstract

The inserts of plasmid cDNA clones for transcripts showing meiotic prophase specific expression show cross reassociation to varying degrees of intensity with one another. These clones were recovered from a cDNA library made from Lilium microsporocyte poly(A)+ RNA. RNA-dot and Northern-blot analyses indicate that these clones represent transcripts specific to the meiotic prophase interval in microsporocytes. The transcripts appear to constitute the most abundant class of meiosis-specific poly(A)+ RNAs. At least two subgroups can be distinguished by examining cloned transcripts from genes of this expressed meiotic prophase repeat (EMPR) sequence family. Members of each subgroup have similar although not identical restriction maps and show relatively high but varying fidelities of DNA cross reassociation between members. However, consensus restriction maps of the two subgroups are largely dissimilar and, except at low stringencies, cross reassociation is readily detected only at restriction fragments from a particular conserved internal segment. The DNA sequence of a representative EMPR clone has been determined, and the inferred peptide product has been found to show extensive sequence homology to that of a small heat-shock gene of Glycine max, particularly in the conserved region. Alignment of the sequences for the conserved regions of two EMPR subgroup representatives with the soybean sequence suggests that selection has acted to conserve similar blocks of amino acids in this area. These observations suggest that a major portion of the transcripts produced during the apparently unrelated processes of meiosis and heat shock in higher plants are derived from related gene sequences encoding similar products.Key words: meiosis, transcription, specific cDNA, heat-shock mRNA.