Panicle exsertion is one of the important agronomic traits, the defect of panicle protrusion usually leads to panicle enclosure, affecting flowering and pollination, resulting in reducing grain yield in rice. Gibberellin plays an important role in regulating rice panicle exsertion, but its regulatory mechanism and network are still largely unclear.

Recently, a research group led by Prof. BU Qingyun from the Northeast Institute of Geography and Agroecology (IGA) of Chinese Academy of Sciences (CAS) revealed that OsWRKY78 regulates panicle exsertion via mediating crosstalk between GA and MAPK signaling pathway.

This work was published in Journal of Integrative Plant Biology on March 13th.

The researchers characterized the oswrky78 mutant, and find that oswrky78 show shorten panicle exsertion, and panicles are enclosed in flag leaf sheath partially. This indicates that WRKY78 regulates rice panicle exsertion.

The panicle enclosure defect of oswrky78 can fully rescue by applying exogenous GA, and the bioactive GAs content in oswrky78 is significantly lower. GA biosynthesis genes OsGA20ox‐1, OsGA20ox‐3 and OsGA3ox‐1 have lower expression, but GA metabolism genes OsGA2ox‐3 and OsGA2ox‐4 have higher expression in oswrky78. OsWRKY78 can bind to the promoter of GA biosynthesis genes and activate its expression, but cannot directly regulate GA metabolism genes. Moreover, overexpression of OsGA20ox‐1 can fully rescue the panicle enclosure of oswrky78. Thus, OsWRKY78 regulates rice panicle exsertion might by directly activate GA biosynthesis but indirectly inhibit GA metabolism.

In addition, OsMAPK6 can interact with and phosphorylate OsWRKY78, and enhance its protein stability. Overexpression of phosphorylation site activation OsWRKY78(SD) and OsWRKY78 can fully rescue the panicle ensertion defect of oswrky78, but overexpression phosphorylation site inactivation OsWRKY78(SA) cannot. These indicating that the phosphorylation of OsWRKY78 by OsMAPK6 is indispensable for its panicle exsertion regulation function.

In summary, this work revealed that OsWRKY78 through regulating GA biosynthesis and GA metabolism regulates rice panicle exsertion. Besides, OsWRKY78 is a phosphorylated substrate of OsMAPK6. The above indicates that OsWRKY78 vis mediating the crosstalk of GA and MAPK signaling in regulating rice panicle exsertion.