Assessment of genetic diversity of cultivated and wild Iranian grape germplasm using retrotransposon-microsatellite amplified polymorphism (REMAP) markers and pomological traits.

Understanding the genetic diversity and relationships between genotypes is an effective step in designing effective breeding programs. Insertional polymorphisms of retrotransposons were studied in 75 cultivated and wild grape genotypes using retrotransposon-microsatellite amplified polymorphism (REMAP) technique. In the morphological part of work, seven pomological traits with a high breeding interest were also analyzed in the cultivated genotypes. A total of 328 markers were produced by 42 primer pairs, out of which 313 markers (95.43%) were polymorphic. Number of markers ranged from 4 in loci Tvv1Fa-873, Vine1-811, Gret1Ra-855 and Tvv1Fa-890 to 12 in locus Vine1Ra-841 with an average value of 7.45. Similarity values based on Dice's coefficient among all 75 grapevine genotypes varied from 0.41 to 0.77. Classification of genotypes using unweighted pair-group method using complete-linkage clustering led to six distinct groups. Some wild and cultivated varieties placed in the same groups. It seems there are close relationship between wild and cultivated genotypes and maybe wild genotypes are ancestor of native grapevines. Grouping of grapevine genotypes based on molecular marker data was not in agreement with clustering by agro-morphological data indicating that the most of multiplied sequences are confined to the non-coding regions of transposon elements. Results showed a substantial level of genetic diversity at molecular and pomological level and the potential of this diversity for future grape breeding programs.

Functional characterization of yeast mitochondrial release factor 1.

The yeast Saccharomyces cerevisiae mitochondrial release factor was expressed from the cloned MRF1 gene, purified from inclusion bodies, and refolded to give functional activity. The gene encoded a factor with release activity that recognized cognate stop codons in a termination assay with mitochondrial ribosomes and in an assay with Escherichia coli ribosomes. The noncognate stop codon, UGA, encoding tryptophan in mitochondria, was recognized weakly in the heterologous assay. The mitochondrial release factor 1 protein bound to bacterial ribosomes and formed a cross-link with the stop codon within a mRNA bound in a termination complex. The affinity was strongly dependent on the identity of stop signal. Two alleles of MRF1 that contained point mutations in a release factor 1 specific region of the primary structure and that in vivo compensated for mutations in the decoding site rRNA of mitochondrial ribosomes were cloned, and the expressed proteins were purified and refolded. The variant proteins showed impaired binding to the ribosome compared with mitochondrial release factor 1. This structural region in release factors is likely to be involved in codon-dependent specific ribosomal interactions.