Transformation of Arabidopsis with a Brassica SLG/SRK region and ARC1 geneis not sufficient to transfer the self-incompatibility phenotype

Self-incompatibility (SI) promotes outbreeding in flowering plants, and in Brassica SI is genetically controlled by the S locus. Self-incompatible Bra ssica and self-fertile Arabidopsis belong to the same crucifer family. In a ddition, a comparative analysis reveals a high degree of microsynteny betwe en the B. campestris S locus and its homologous region in Arabidopsis - wit h the notable exception that the Brassica SI genes, SLG and SRK, are missin g. Brassica ARCI encodes a component of the SRK signal transduction pathway leading to self-pollen rejection, and no closely related ARC1 homolog has been identified in Arabidopsis. The purpose of the research reported here w as to introduce Brassica SI components into Arabidopsis in an attempt to co mpensate for the missing genes and to investigate whether the SI phenotype can be transferred. Inserts of approximately 40 kb from the fosmid clones F 20 and F22, which span the B. napus W1 SLG-SRK region, were cloned into the plant transformation vector pBIBAC2. Transgenic plants were generated that expressed the Brassica SI genes in the flower buds. In addition, the endog enous, SLG-like, gene AtS1 was not co-suppressed by the Brassica SLG transg ene. No SI phenotype was observed among the T1 BIBAC2-F20 and BIBAC2-F22 tr ansgenic plants. When the ARCI gene was transformed into BIBAC2-F20 or BIBA C2-F22 plants. the resulting BIBAC2-F20-ARC1 and BIBAC2-F22-ARC1 plants sti ll set seeds normally, and no rejection response was observed when self-inc ompatible B. napus W1 pollen was placed on BIBAC2-F20-ARC1 or BIBAC2-F22-AR C1 Arabidopsis stigmas. Taken together, our results suggest that complement ing Arabidopsis genome with Brassica SLC, SRK and ARC1 genes is unlikely to be sufficient to transfer the SI phenotype.