GA Regulates Nitrogen-mediated Tillering Responses In Rice

Rice is one of the most important crops in the world.As people's increasing demand for food,both increasing rice yield and improving rice environmental adaptability are important approaches to ensure food security.In the 60s of the last century,the use of sdl gene triggered a green revolution in rice,which significantly increased rice yield.sd1 can significantly decrease plant height and enhance lodging-resistance capability,which could reduce grain loss and improve harvest index.We also found that sdl can increase the number of tillers in rice,and changed the response of rice tillers to nitrogen.Although the molecular mechanism of sdl reduces rice plant height has been deeply elucidated,the molecular mechanisms of sd1 increasing the number of tillers in rice and changing the responses of rice tillers to low nitrogen remain largely unknown.In this study,we found a rice mutant ngr5 whose tiller number could not response to the change of nitrogen concentration.We cloned and characterized NGR5 by map-based cloning.It was found that the expression level of NGR5 was induced by nitrogen,and nitrogen induced the protein level of NGR5 accumulation.Using yeast-two hybrid screening,several NGR5-interacting proteins were identified,incoulding SLR1 and LC2.Further studies showed that the tiller numbers of slrl and lc2 also lost responses to nitrogen.The accumulation of SLR1 protein was induced by nitrogen.Besides that,SLR1 could increase the stability of NGR5.Therefore,SLR1 and LC2 are important components of rice response to nitrogen.ChIP analysis showed NGR5 protein could bind to D14 and SPL14 loci.The expressions of D14 and SPL14 were repressed by nitrogen in WT,but not in ngr5.At different concentrations of nitrogen,the expressions of D14 and SPL14 in 9311-SD1 were all higher than those of D14 and SPL14 in 9311-sd1.The gene expressions of D14 and SPL14 in 9311-sd1 were significantly inhibited by the increase of nitrogen concentration,while in 9311-SD1 they were not significantly inhibited.Further studies showed that there are many hidtone modifications,H3K27me3,at the D14 and SPL14 loci,which depends on NGR5 and SLR1 proteins.Moreover,the levels of H3K27me3 modification at D14 and SPL14 loci were induced by nitrogen.Under different concentrations of nitrogen,the levels of H3K27me3 at D14 and SPL14 in 9311-SD1 were lower than those in 9311-sd1,and hardly induced by nitrogen.While in 9311-sd1,the levels were also increased with the increase of nitrogen concentration,Above all,NGR5 is a key component in the response of rice tillers to nitrogen,sd1 is involved in controliling tillers of rice through SLR1-NGR5-PRC2 pathway,thus maintaining more tillers even in low nitrogen environment.This study will not only help us understand the molecular mechanism of rice tillering regulated by nitrogen,but also provide ideas for improving the environmental adaptability of rice in breeding research.