Comparative mapping of apomixis in Paspalum

PUPILLI, FULVIO; CALDERINI, ORNELLA; BUSTI, ALEXANDRA; MARTÍNEZ, ERIC J.; QUARIN, CAMILO L.; ARCIONI, SERGIO

Monte Verità, Ascona

Congreso; Gametophytes-Evolution, Development and Function; 2003

Apomixis is a reproductive process that in more than 400 species circumvents female meiosis and fertilization of egg cells and results to seed-derived progeny genetically identical to the mother plant. A comparative mapping approach was undertaken to isolated the genetic determinants of apomixis in three wild apomictic grass species belonging to the Paspalum genus. Both rice anchor markers and homologous Paspalum probes were used to map apomixis in the two closely related species P. simplex and P. malacophyllum and in the more distantly related species P. notatum. The comparative mapping analysis showed that the apo locus is characterised by strong repression of recombination and sinteny with the rice genome in all the 3 species. However, whereas the apo-locus of P. simplex and P. malacophyllum showed a strict collinearity of markers with the telomeric part of the long arm of rice chromosome 12, this sinteny was only partially conserved in P. notatum. In particular in the latter species, only a sub portion of the apo-locus of P. simplex, which was identified by three rice markers and one homologous probe, was also related to the apomictic reproduction in P. notatum in which other three rice markers mapped in the long arm of rice chromosome 2 showed linkage with apomixis. Based on the analysis of linkage relationships among sexual alleles which were orthologous to the apo-linked ones we argued that in P. notatum a sub portion of the apo-locus of P. simplex has been translocated from the homoeologous of the rice chromosome 12 to the correspondent rice chromosome 2 background. This translocation occurred within the same species and had two main consequences i) the induction of apomixis from sexuality and ii) the repression of recombination in the nearness of the insertion site. On the basis of these results we believe that the portion of the apo-locus of P. simplex which was subjected to the translocation in P. notatum is a promising source of candidate genes for apomixis and therefore we foccussed our efforts on the isolation and characterisation of genes that are present in this area by the expression analysis of: i) some Arabidopsis genes that are homeologous to the rice ESTs linked to apomixis and ii) homologous genes isolated from a BAC library of apomictic P. simplex.