Ethylene plays important roles in plant growth, development and stress responses. The ethylene signaling pathway has been extensively studied mainly in Arabidopsis. However，the molecular mechanism of ethylene signaling is largely unknown in rice.

 

Prof ZHANG Jinsong’s group and Prof CHEN Shouyi’s group at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, have isolated a set of rice ethylene-response mutants in previous studies and now they further characterized the mutant mhz6.

 

Through map-based cloning, they found that MHZ6 encodes OsEIL1, a rice homolog of EIN3, which is the master transcriptional regulator of ethylene signaling in Arabidopsis. Disruption of MHZ6/OsEIL1 caused ethylene insensitivity mainly in roots, whereas silencing of the closely-related OsEIL2 led to ethylene insensitivity mainly in coleoptiles of etiolated seedlings.

 

This organ-specific functional divergence is different from the functional features of EIN3 and EIL1, both of which mediate the incomplete ethylene-responses of Arabidopsis etiolated seedlings. In Arabidopsis, EIN3 and EIL1 play positive roles in plant salt tolerance. In rice, however, lack of MHZ6/OsEIL1 or OsEIL2 functions improves salt tolerance, whereas the overexpression lines exhibits salt hypersensitivity at seedling stage, indicating that MHZ6/OsEIL1 and OsEIL2 negatively regulate salt tolerance in rice. Furthermore, this negative regulation by MHZ6/OsEIL1 and OsEIL2 in salt tolerance is likely in part attributable to the direct regulation of OsHKT2;1 expression and Na⁺ uptake in roots (Figure 1). Additionally, MHZ6/OsEIL1 overexpression promotes grain size and thousand-grain-weight.

 

Together, this study provides insights for functional diversification of MHZ6/OsEIL1 and OsEIL2 in ethylene response and finds a novel mode of ethylene-regulated salt stress response which could be helpful for engineering salt-tolerant crops.

The paper has been published online on May 20, 2015, in Plant Physiology (DOI:10.1104/pp.15.00353). Dr. YANG Chao and Dr. MA Biao are the co-first authors of the paper. This work is supported by National Natural Science Foundation of China, 973 projects and some other funding agencies.

 

 

In rice, MHZ/OsEIL1 and OsEIL2 regulate ethylene responses of roots and coleoptiles respectively. Both can activate OsHKT2;1 expression to promote Na uptake for ion homeostasis under water environment. However, under high salinity, the rice plants with enhanced ethylene signaling will be sensitive to salt stress. In Arabidopsis, EIN3 and EIL1 show no organ-specificity in regulation of ethylene response but promote salt tolerance. (Image by IGDB)