Crosstalk Between Ethylene and JA/ABA/Sugar Signalling in Plants Under Physiological and Stress Conditions.

Growth, development and defence responses of plants are governed through signalling networks that connect inputs from nutrient status, hormone cues and environmental signals. Plant hormones as endogenous signals are essential for modulating plant defence responses and developmental processes. Ethylene (ET), a gaseous hormone, is widely established as a regulator of these processes. Over the last two decades, substantial research reports have revealed the interaction between ET and other endogenous cues, including abscisic acid (ABA), sugars and jasmonates (JAs). However, these reports showed numerous conflicting or contrasting conclusions. For example, some reports revealed that ET and ABA/sugar/JA signalling synergistically regulate plant growth, development and defence responses, whereas other reports demonstrated that these cues antagonistically modulate these processes. This suggests that the crosstalk between ET and JA/ABA/sugar signalling is very complex, that is, these hormones can function either antagonistically or coordinately, dependent on the given biological process (e.g., under physiological or stress conditions). Further analysis found that whether synergistic or antagonistic actions exist between ET and JA/ABA/sugar signalling is determined by the induction/inhibition of their respective master transcription factors in these pathways. We here summarise the most recent advances and outstanding questions and/or challenges in the area of crosstalk between ET and ABA/sugar/JA signalling under physiological or stress conditions.