Background: Polyploidy has long been recognized as playing an important role in plant evolution. In floweringplants, the major route of polyploidization is suggested to be sexual through gametes with somatic chromosomenumber (2n). Parallel Spindle1 gene in Arabidopsis thaliana (AtPS1) was recently demonstrated to control spindleorientation in the 2nd division of meiosis and, when mutated, to induce 2n pollen. Interestingly, AtPS1 encodes aprotein with a FHA domain and PINc domain putatively involved in RNA decay (i.e. Nonsense Mediated mRNADecay). In potato, 2n pollen depending on parallel spindles was described long time ago but the responsible genehas never been isolated. The knowledge derived from AtPS1 as well as the availability of genome sequences makesit possible to isolate potato PSLike (PSL) and to highlight the evolution of PSL family in plants.Results: Our work leading to the first characterization of PSLs in potato showed a greater PSL complexity in thisspecies respect to Arabidopsis thaliana. Indeed, a genomic PSL locus and seven cDNAs affected by alternativesplicing have been cloned. In addition, the occurrence of at least two other PSL loci in potato was suggested bythe sequence comparison of alternatively spliced transcripts.Phylogenetic analysis on 20 Viridaeplantae showed the wide distribution of PSLs throughout the species and theoccurrence of multiple copies only in potato and soybean.The analysis of PSLFHA and PSLPINc domains evidenced that, in terms of secondary structure, a major degree ofvariability occurred in PINc domain respect to FHA. In terms of specific active sites, both domains showeddiversification among plant species that could be related to a functional diversification among PSL genes. Inaddition, some specific active sites were strongly conserved among plants as supported by sequence alignmentand by evidence of negative selection evaluated as difference between non-synonymous and synonymousmutations.Conclusions: In this study, we highlight the existence of PSLs throughout Viridaeplantae, from mosses to higherplants. We provide evidence that PSLs occur mostly as singleton in the analyzed genomes except in soybean andpotato both characterized by a recent whole genome duplication event. In potato, we suggest the candidate PSLgene having a role in 2n pollen that should be deeply investigated.We provide useful insight into evolutionary conservation of FHA and PINc domains throughout plant PSLs whichsuggest a fundamental role of these domains for PSL function.
