Functional characterization of Parallel Spindles Like (PSL) genes in potato.

In plants, whole-genome doubling largely contributed to plant evolution and diversification. Gametes with somatic chromosome number (2n) are widely recognized as the major route of plant polyploidization. The parallel arrangement of the spindles (ps) in the 2nd division of male meiosis is the most common mechanism generating 2n pollen through the formation of dyads and triads. In Arabidopsis, Parallel Spindle1 (AtPS1) was reported as implicated in the control of the ps meiotic defect. We identified three Parallel Spindle Like loci (PSL1-3) in the potato genome. To establish their putative role in the formation of 2n male gametes, two functional strategies were undertaken. Firstly, the Arabidopsis mutant Atps1, kindly given by Dr. R. Mercier (INRA, Versailles), was transformed with a construct containing the PSL3 gene. The PSL3 gene expression was detected by qRT-PCR in the Atps1 transgenic lines. However, these lines still showed the mutant phenotype, i.e. dyads and triads, thereby indicating that the transgene, PSL3, failed to functionally complement the Atps1 mutation. In the other strategy, RNAi silencing of PSLs was performed in a wild diploid species (Solanum commersonii) and in a tetraploid potato (S. tuberosum cv Desirée). Hairpin-RNAi expression vector containing a 400 bp sequence common to all PSLs was utilized for transformation experiments by Agrobacterium tumefaciens. Several transgenic plants from both species have been obtained. The silencing of PSL1 was confirmed in leaf by qRT-PCR. PSLs silencing in floral buds and pollen ploidy are under evaluation.