Structural diversity of the patatin gene family in potato cv. Desiree.

We have used a combined genetical and molecular approach to study the structural diversity of the patatin gene family in tetraploid Solanum tuberosum L. cv. Desiree (2n = 4x = 48). Nine dihaploid derivatives (2n = 2x = 24) of cv. Desiree were isolated by gynogenesis through prickle pollination with S. phureja Juz et Buk. Patatin DNA sequences in Desiree and in the dihaploids were examined by probing Southern blots of restriction endonucleases HindIII and XbaI digested DNA with patatin cDNA region-specific gene probes and by more detailed examination (restriction endonuclease mapping and partial DNA sequencing) of 10 patatin genomic clones in bacteriophage lambda replacement vector EMBL4. This provided positive identification for most individual patatin gene family members and some estimate of their organisation and diversity. Most of the 64-72 patatin DNA copies showed little allelic variation based on HindIII and XbaI restriction fragment length polymorphism (RFLP) mapping and did not appear to be very tightly clustered. Four of the 6-8 class I patatin genes (without a characteristic 22 bp insert in their untranslated leader DNA), showed apparent allelic homogeneity, whilst the remaining class I genes comigrated with a single class II patatin gene RFLP subclass. Of the isolated clones, 4 contained apparent pseudogenes lacking 5' control sequences and exon-1 DNA while another clone contained a patatin gene truncated at the 5' region due to the cloning event. The remaining 5 all contained class II genes (with the 22 bp insert) and these showed varying degrees of sequence homology for 400 bp of conserved 5' coding and non-coding DNA (from 77%-95%). In one case the extent of homology differed, with complete sequence divergence upstream of position -80 from the start of transcription. The structural diversity of the patatin gene family is discussed in relation to expression of individual patatin genes and the use of cv. Desiree as a host for potato transformation experiments.