The role of CLE peptides in suppression of mycorrhizal colonisation of tomato.

Symbioses with beneficial microbes are widespread in plants, but these relationships must balance the energy invested by the plants with the nutrients acquired. Symbiosis with arbuscular mycorrhizal (AM) fungi occurs throughout land plants but our understanding of the genes and signals that regulate colonisation levels is limited, especially in non-legumes. Here, we demonstrate that in tomato two CLV3/EMBRYO-SURROUNDING REGION (CLE) peptides, SlCLE10 and SlCLE11, act to suppress AM colonisation of roots. Mutant studies and over expression via hairy transformation indicate SlCLE11 acts locally in the root to limit AM colonisation. Indeed, SlCLE11 expression is strongly induced in AM colonised roots but SlCLE11 is not required for phosphate suppression of AM colonisation. SlCLE11 requires the FIN gene that encodes an enzyme required for CLE peptide arabinosylation to suppress mycorrhizal colonisation. However, SlCLE11 suppression of AM does not require two CLE receptors with roles in regulating AM colonisation, SlFAB (CLAVATA1 orthologue) or SlCLV2. Indeed, multiple parallel pathways appear to suppress mycorrhizal colonisation in tomato, as double mutant studies indicate SlCLV2 and FIN have an additive influence on mycorrhizal colonisation. SlCLE10 appears to play a more minor or redundant role, as cle10 mutants did not influence intraradical AM colonisation. However, the fact that cle10 mutants had elevated number of hyphopodia and that ectopic over expression of SlCLE10 did suppress colonisation suggests SlCLE10 may also play a role in regulating AM colonisation. Our findings show that CLE peptides regulate AM colonisation in tomato and at least SlCLE11 likely requires arabinosylation for activity.