FIGURE 3.

Diverse roles of ethylene in regulating agronomic traits in rice. In rice, ethylene regulates a wide variety of major agronomic traits ranging from emerging from the soil to grain filling and senescence. Ethylene promotes growth of coleoptiles/mesocotyls by partially inhibiting JA biosynthesis. In contrast, JA promotes rice leaf senescence through a cascade of OsCOI1b-OsJAZ-OsEIN3-OsORE1. JA and ethylene synergistically accelerate rice leaf senescence by activating common and differential SAGs. Ethylene positively regulates rice grain size/weight, flowering, tillering and leaf angle but negatively affects rice grain filling and salt tolerance. The lower ratio of ethylene to ABA is beneficial for rice grain filling. Upon submergence, SUB1A negatively regulates GA response by inhibiting the degradation of SLR1/SLRL1 to restrict plant growth in submergence-tolerance species. On the contrary, ethylene promotes internode elongation through increasing transcription of SK1/2 and GA production to escape flooding in deepwater rice. OsGI1, OsGIGANTEA1; RCN1, TERMINAL FLOWER1/CENTRORADIALIS-like; GY1/EG1, GAOYAO/EXTRA GLUME; HKT2;1, HIGH-AFFINITY K⁺ TRANSPORTER2;1; SLR1, Slender Rice-1; SLRL1 SLR-like 1; ABA, abscisic acid; GA, gibberellin; JA, jasmonate; COI1, coronatine insensitive 1; JAZ, jasmonate ZIM-domain protein. Blue lines indicate the leaf senescence regulatory pathway. Purple lines indicate the submergence tolerance regulatory pathway. Arrows and T-bars indicate direct or indirect activation and suppression, respectively. Dotted lines indicate several or unknown steps involved in the pathway.