Fig. 4.

The interplay of ABA and other phytohormones (GA, ET, SA, BR, and Auxin) signaling in the regulation of seed germination and post-germination growth. ABA crosstalks with other phytohormones either by affecting their biosynthesis or by interfering with their signaling pathways during germination and post-germination growth. Among these, the interaction between ABA and GA is most studied and important. FUS3 and ABI4 play more vital roles to mediate the antagonism between ABA and GA. SA was found to regulate the content of ABA negatively and GA positively, respectively in seed germination. Both two factors LFL and CHO1 were showed inhibition to GA synthesis to involve seed germination regulation. After that, some downstream factors of GA such as SPY, SNY, SLY, SIZ, RGL2, etc. display different functions in the crosstalk between GA and ABA. Both SIZ and RGL2 can repress and promote ABI5, respectively. Besides, RGL2 can be degraded by CSN1 and regulate ABI5 together with an NF-CY factor. ABA-mediating ABI3, ABI5, and RGL2 regulate MFT by establishing a negative feedback loop to modulate the ABA and GA antagonism, in which, MFT also inhibits ABI5. A study indicated that auxin stimulates ABI3 expression through ARF10 and ARF16 indirectly, which connects the ABA and auxin in seed germination regulation. In some ways, ABA inhibits ACO and ACS to influence ethylene synthesis negatively. Meantime, ETR1/2 and histone deacetylation cofactors SNL1/2 mediate the antagonism between the ABA and ethylene to involve seed germination, in which some ERF factors are involved. BR promotes seed germination as well as inhibits BIN2, which interacts with ABI5 and positively regulates ABA responses during seed germination and post-germination. Activated and repressive effects are shown by arrows and bars, respectively.