Expression analyses of sweet cherry AUX/IAAs and involvements of PavAUX/IAA9/11 in regulating fruitlet abscission.

Key message: The sweet cherry genome contains 25 AUX/IAA members, of which PavAUX/IAA9 and PavAUX/IAA11 negatively and positively regulate fruitlet abscission, respectively. The auxin/indole-3-acetic acid (AUX/IAA) gene family is plant-specific and plays various roles in growth and development. However, its function in sweet cherry fruitlet abscission remains unclear. This study identified 25 AUX/IAA members in the sweet cherry (Prunus avium L.) genome, which exhibit conserved gene structures and are subjected to purifying selection. The promoter regions of these genes contain numerous auxin response-related cis-regulatory elements. RNA-seq and RT-qPCR analyses revealed that several genes, including PavAUX/IAA9, were down-regulated, whereas PavAUX/IAA11 was up-regulated during the fruitlet abscission. Both PavAUX/IAA9 and PavAUX/IAA11 are nuclear-localized proteins, and their overexpression in Arabidopsis thaliana alters growth-related phenotypes, and delays or promotes petal abscission, respectively. Yeast two-hybrid (Y2H) and luciferase complementation imaging (LCI) assays demonstrated that PavAUX/IAA9 interacts with itself and with PavTMP87. Yeast one-hybrid and dual-luciferase reporter assays demonstrated that PavARF4 and PavWRKY40 interact with the promoters of PavAUX/IAA9 and PavAUX/IAA11, respectively. PavARF4 and PavWRKY40 lack transcriptional activation activity in yeast systems, suggesting that they function as transcriptional repressors. The regulation of AUX/IAAs expression by sweet cherry ARF and WRKY transcription factors, coupled with the interaction between AUX/IAA and transmembrane proteins (such as PavTMP87), suggests a complex auxin signaling pathway involved in fruitlet abscission in sweet cherry. This highlights the critical regulatory function of AUX/IAA proteins in plant organ abscission.