Identification of genes differentially expressed in inflorescences of sexual and aposporous Paspalum notatum

LASPINA N; VEGA T; ORTIZ JPA; PODIO M; STEIN J; QUARIN CL; ECHENIQUE V; PESSINO SC

Wernigerode, Alemania

Congreso; 3rd International Apomixis Conference Wernigerode Germany; 2007

IPK Gatersleben Alemania. Universidad de Perugia Italia

Paspalum notatum is a warm-season forage grass with mainly diploid (2n=20) and tetraploid (2n=40) representatives. Diploid races reproduce sexually and require cross-pollination, while autotetraploids are self-fertile pseudogamous aposporous apomicts. Although tetraploid sexual individuals have never been found in nature, they could be obtained experimentally by chromosome doubling of sexual diploids. The objective of this work was to carry out a full-transcriptome survey in order to isolate genes differentially expressed in immature inflorescences of sexual and aposporous Paspalum notatum genotypes. For comparisons we used two tetraploid individuals with different reproductive modes, and a derived F1 progeny segregating for apomixis. Differential display experiments were used to check the expression of around 10,000 transcripts. Selection of polymorphic bands allowed the identification of 71 unigenes expressed either in the aposporous or in the sexual genotype. Functional annotation was achieved for 39 of them, while the remaining 32 showed no significant homologies in the genetic databases. Most of the annotated sequences grouped in a few functional categories: 1) signal transduction, particularly components of ERK (extracellular receptor kinase) cascades; 2) nuclear receptor signaling; 3) transcriptional control; 4) transposition and 5) chromatin structure regulation. The apo-specific genes matched preferentially with sequences located onto rice Chr 3 and 11, while the sex-specific sequences frequently mapped to rice Chr 2 long arm, around a region reported to be syntenic with the apo-locus in Brachiaria brizantha and Paspalum notatum. Two of the genes belonging to the latter group generated RFLP and SSCP specific bands cosegregating with apomixis when mapped in Paspalum notatum, suggesting that a particular genetic constitution might induce silencing in the apomictic plants. Our results indicated that a number of genes mapping close to the apo locus in Paspalum might be silenced in apomictic plants but expressed in sexual ones. We also showed evidence that expression modulation of several ERK cascade components is associated with the occurrence of apospory.