The peach (Prunus persica [L.] Batsch) homeobox gene KNOPE3, which encodes a class 2 knotted-like transcription factor, is regulated during leaf development and triggered by sugars

Class 1 KNOTTED1-like transcription factors(KNOX) are known to regulate plant development,whereas information on class 2 KNOX has been limited.The peach KNOPE3 gene was cloned, belonged to a familyof few class 2 members and was located at 66 cM in thePrunus spp. G1 linkage-group. The mRNA localizationwas diversified in leaf, stem, flower and drupe, but recurredin all organ sieves, suggesting a role in sap nutrienttransport. During leaf development, the mRNA earliestlocalized to primordia sieves and subsequently to mesophyllcells of growing leaves. Consistently, its abundanceaugmented with leaf expansion. The transcription wasmonitored in leaves responding to darkening, supply andtransport block of sugars. It peaked at 4 h after darknessand dropped under prolonged obscurity, showing a similarkinetic to that of sucrose content variation. Feeding leafletsvia the transpiration stream caused KNOPE3 up-regulationat 3 h after fructose, glucose and sucrose absorption and at12 h after sorbitol. In girdling experiments, leaf KNOPE3was triggered from 6 h onwards along with sucrose andsorbitol raise. Both the phloem-associated expression andsugar-specific gene modulation suggest that KNOPE3 mayplay a role in sugar translocation during the development ofagro-relevant organs such as drupe.