Peach (Prunus persica [L.] Batsch) KNOPE1, a class 1 KNOX orthologue to Arabidopsis BREVIPEDICELLUS/KNAT1, is misexpressed during hyperplasia of leaf curl disease

Class 1 KNOTTED-like (KNOX) transcription factors control cell meristematic identity. An investigation was carried out to determine whether they maintain this function in peach plants and might act in leaf curliness caused by the ascomycete Taphrina deformans. KNOPE1 function was assessed by overexpression in Arabidopsis and by yeast two-hybrid assays with Arabidopsis BELL proteins. Subsequently, KNOPE1 mRNA and zeatin localization was monitored during leaf curl disease. KNOPE1 and Arabidopsis BREVIPE- DICELLUS (BP) proteins fell into the same phyletic group and recognized the same BELL factors. 35S:KNOPE1 Arabidopsis lines exhibited altered traits resembling those of BP-overexpressing lines. In peach shoot apical meristem, KNOPE1 was expressed in the peripheral and central zones but not in leaf primordia, identically to the BP expression pattern. These results strongly suggest that KNOPE1 must be down-regu- lated for leaf initiation and that it can control cell meristem identity equally as well as all class 1 KNOX genes. Leaves attacked by T. deformans share histo- logical alterations with class 1 KNOX-overexpressing leaves, including cell proliferation and loss of cell differentiation. Both KNOPE1 and a cytokinin synthe- sis ISOPENTENYLTRANSFERASE gene were found to palisade cells interacting with subepidermal mycelium, while zeatin vascular localization was unaltered com- pared with healthy leaves. Subsequently, when myce- lium colonization and asci development occurred, both KNOPE1 and zeatin signals were scattered in sectors of cell disorders. These results suggest that KNOPE1 misexpression and de novo zeatin synthesis of host origin might participate in hyperplasia of leaf curl disease