Figure 3.

Schematic diagram of ethylene-independent function of ACC, EIN2, and EIN3 in Arabidopsis. Upon pollination, ACC functions in pollen tube attraction in an ethylene-independent manner, as the failure of pollen tube attraction in ACS octuplet mutant could not be rescued by ethylene gas treatment [75]. The successful fertilization depends on the dosage effect of the ethylene signaling, as either enhanced accumulation of EIN3 or deletion of EIN2-EIN3/EIL1 shows compromised fertilization [70–72]. In parallel, fertilization stimulates EIN3 accumulation to trigger synergid cell death by an unknown factor [74]. Besides, EIN2, the central component of the ethylene pathway, participates in the mTOR-glucose signaling pathway in an ethylene-independent manner [73], while it needs further investigation to see whether the mTOR-EIN2-glucose signaling module gets involved in fruit set. The regular arrow indicates positive regulation, and the ‘T’ represents negative regulation.