The auxin response factor PgARF19 directly activates PgFLP and PgPIN3 to regulate the GSA of adventitious roots in self-rooted pomegranate stocks

Pomegranate ( Punica granatum L.) has abundant germplasm resources and strong adaptability, which has high ornamental value, good ecological and economic benefits, and high health care functions. The main production method of pomegranate industry in China is to build orchards with self-rooted stocks. However, the gravitropic setpoint angle (GSA) of self-rooted pomegranate stocks adventitious roots are relatively large, and its root system is shallow, resulting in poor stress resistance of pomegranate. Therefore, understanding the molecular basis of gravitropism in adventitious roots of self-rooted pomegranate stocks is crucial for breeding deep-rooted cultivars. This study identifies PgARF19 as a key auxin response factor that modulates the GSA in the self-rooted pomegranate stocks adventitious roots. We demonstrate that PgARF19 directly activates the transcription of PgFLP and PgPIN3 via binding to their promoters, thereby regulating the adventitious roots GSA. Additionally, the self-rooted pomegranate stocks adventitious root gravitropism has been abolished under microgravity. Furthermore, the 35S:PgARF19 in Arabidopsis enhanced lateral root gravitropism, resulting a smaller GSA, which confirms its conserved function via PgFLP and PgPIN3 in pomegranate. These results reveal a novel transcriptional regulatory module, PgARF19-PgFLP/PgPIN3, regulating the GSA of self-rooted pomegranate stocks adventitious roots in response to gravity.