Static Magnetic Field Promotes Wheat Nitrogen Assimilation by Repressing Jasmonates Biosynthesis Through <scp>TaHY5</scp>

The magnetic field is a continuously present environmental factor. It has been found that many species, including plants, can sense and utilise it. However, the effects of the magnetic field on plants and its potential utilisation, especially in crops, have been little explored. Here, we found that static magnetic field (SMF) treatment increased wheat growth regardless of the magnetic field polarity. Specifically, the root system of wheat increased dramatically in both root number and length in a magnetic field strength-dependent manner, leading to higher fresh biomass in plants subjected to SMF treatment. Concurrently, the expression profile showed enrichment in nitrogen (N), jasmonates (JAs) and light signalling pathways under SMF treatment. Indeed, wheat N uptake was enhanced by SMF, and JAs content was dramatically reduced in magnetically treated wheat seedlings, consistent with the downregulation of JAs biosynthesis genes. Furthermore, this magnetic repression of JAs was abolished in dark conditions. We further demonstrated that SMF also induced the light signalling pathway, including the core transcription factor HY5, which directly binds to the promoters of JAs biosynthesis genes (LOX2, OPR3 and JAR1) and represses their expression by recruitment of HDA9. Consistently, JA application and hy5 knock out blocked SMF effect on wheat N absorption. Finally, SMF repressed JAs by HY5 recruitment of HDA9 to deacetylation of JAs biosynthesis gene sites. These results demonstrated a new finding of the magnetic signalling pathway in plants and implied a great potential for utilising magnets to promote N use efficiency in wheat.