Cold-induced miR166 leads to SlHB15 dosage sensitivity, aberrant ovule development and fruit set in tomato. Cloning and expression studies of PF1/ SlHB15

Fruit set is inhibited by adverse temperatures, with consequences on yield. We isolated a tomato mutant producing fruits without pollination under heat and cold stresses and identified the causal gene as SlHB15, belonging to class-III homeodomain leucine-zipper transcription factors. SlHB15 is expressed in the ovule integument, binds the promoters of auxin genes to repress auxin signaling and to ethylene genes to activate their expression. At cold, SlHB15 is subjected to conditional gene-dosage regulation controlled by miR166. Knockdown of SlHB15 alleles by miR166 lead to a continuum of aberrant ovules that mimic transcriptional changes occurring in fertilized ovules. Our finding demonstrates the role of SlHB15 as sentinel to prevent fruit set in absence of fertilization and its use as a target of enhancing fruiting under extreme temperatures.