Characterization and expression analysis of somatic embryogenesis receptor kinase (SERK) genes in sexual and apomictic paspalum notatum

Abstract

The SOMATIC EMBRYOGENESIS RECEPTOR- LIKE KINASE (SERK) gene plays a fundamental role in

somatic embryogenesis of angiosperms, and is associated with apomixis in Poa pratensis. The objective of this work

was to isolate, characterize and analyze the expression pat- terns of SERK genes in apomictic and sexual genotypes of

Paspalum notatum. A conserved 200-bp gene fragment was amplified from genomic DNA with heterologous primers, and used to initiate a chromosomal walking strategy for cloning the complete sequence. This procedure allowed the isolation of two members of the P. notatum SERK family; PnSERK1, which is similar to PpSERK1, and PnSERK2, which is similar to ZmSERK2 and AtSERK1. Phylogenetic analyses indicated that PnSERK1 and PnSERK2 represent

paralogous sequences. Southern-blot hybridization indi- cated the presence of at least three copies of SERK genes

in the species. qRT-PCR analyses revealed that PnSERK2 was expressed at significantly higher levels than PnSERK1 in roots, leaves, reproductive tissues and embryogenic calli.Moreover, in situ hybridization experiments revealed that PnSERK2 displayed a spatially and chronologically altered

expression pattern in reproductive organs of the apom- ictic genotype with respect to the sexual one. PnSERK2

is expressed in nucellar cells of the apomictic genotype at meiosis, but only in the megaspore mother cell in the sexual genotype. Therefore, apomixis onset in P. notatum seems to be correlated with the expression of PnSERK2 in nucellar tissue.