CpARF2 and CpEIL1 interact to mediate auxin-ethylene interaction and regulate fruit ripening in papaya.

Papaya (Carica papaya L.) is a commercially important fruit crop. Various phytohormones, particularly ethylene and auxin, control papaya fruit ripening. However, little is known about the interaction between auxin and ethylene signaling during the fruit ripening process. In the present study, we determined that the interaction between the CpARF2 and CpEIL1 mediates the interaction between auxin and ethylene signaling to regulate fruit ripening in papaya. We identified the ethylene-induced auxin response factor CpARF2 and demonstrated that it is essential for fruit ripening in papaya. CpARF2 interacts with an important ethylene signal transcription factor CpEIL1, thus increasing the CpEIL1-mediated transcription of the fruit ripening-associated genes CpACS1, CpACO1, CpXTH12 and CpPE51. Moreover, CpEIL1 is ubiquitinated by CpEBF1 and is degraded through the 26S proteasome pathway. However, CpARF2 weakens the CpEBF1-CpEIL1 interaction and interferes with CpEBF1-mediated degradation of CpEIL1, promoting fruit ripening. Therefore, CpARF2 functions as an integrator in the auxin-ethylene interaction and regulates fruit ripening by stabilizing CpEIL1 protein and promoting the transcriptional activity of CpEIL1. To our knowledge, we have revealed a novel module of CpARF2/CpEIL1/CpEBF1 that fine-tune fruit ripening in papaya. Manipulating this mechanism could help growers tightly control papaya fruit ripening and prolong shelf life.