Nitrogen Uptake And Translocation In Response To Potassium Treatments And Functional Analysis Of Potassium Channel OsSKOR In Rice

Nitrogen and potassium are essential nutrients for rice,and nitrogen and potassium fertilizers are the most input fertilizers during rice production.Meanwhile,potassium fertilizer affects the utilization of nitrogen,and the combined application of nitrogen and potassium fertilizers could increase grain yield and improve fertilizer use efficiency.Physiologically,nitrogen and potassium utilization needs uptake by roots and the subsequent translocation within rice plants.These processes required specific transporters and some important regulatory factors,which further affect the metabolism process,the growth and development of rice,as well as the grain yield and quality.However,the details of nitrogen utilization regulated by potassium nutrition are still unclear.Thus,this research focuses on the physiological and molecular mechanisms of nitrogen uptake and translocation in response to the external potassium level,and the effect of potassium distribution on nitrogen utilization via the functional analysis of potassium channel SKOR.The results of the study are as follows:（1）Potassium is effective involved in regulating the uptake and transport of nitrogen.Low potassium inhibits the uptake and transport of NO₃-N and promotes the uptake and transport of NH₄-N.High potassium promotes the uptake and transport of NO₃-N and inhibits the uptake and transport of NH₄-N.The transport intensity of amino acids from roots to shoots showed a positively correlation with the external potassium level.Transcriptome sequencing and q RT-PCR analysis showed that members of nitrate,ammonium and amino acid transporters are participate in adapting to external potassium level.Further research on the functions of these genes will help to uncover the detailed mechanism of rice nitrogen uptake and transport in response to potassium level.Additionally,nitrate reduction,glutamine and asparagine synthesis pathways could response to potassium treatments;further participating in adapting to external potassium and then regulating nitrogen utilization in rice.（2）OsSKOR has two different transcript forms in rice,named OsSKOR.1 and OsSKOR.2.OsSKOR.1 covers all the coding information of OsSKOR.2 and another 849coding bases in the front end of OsSKOR.2.Like other Shaker family members,OsSKOR.1possesses six-time transmembrane structures,and the amino acid sequences of those proteins have 5 conserved motif in rice.Further analysis identified the potential phosphorylated sites of OsSKOR.1,and the possible interacting proteins of OsSKOR including phosphokinase and ubiquitin ligase.Cis-acting elements analysis found ABA,Me JA,GA and adversity stress regulated elements in the promoter region of OsSKOR,which indicated that the expression of OsSKOR might regulated by a variety of hormone signals.Moreover,expression of OsSKOR in roots is much higher than that in other tissues,and changed little by external nitrogen,phosphorus,potassium and other nutritional deficiency signals.（3）The expression of OsSKOR was induced by external high nitrogen.SKOR knock-out mutants were constructed using CRISPR-Cas9 technology,and two frameshifts OsSKOR-CRISPR lines（skor-1 and skor-2）were selected.Further phenotype analysis showed that disruption of SKOR lead to a shorter root length,and this phenotype closely related to external potassium or nitrogen treatments,as potassium deficiency or high potassium or high nitrogen treatments could cause this difference to shrink or even disappear.Moreover,loss function of SKOR hardly affected the potassium ion content in the shoots of rice,but decreased nitrate content in the shoots.The above research results not only provide important reference for understanding the details of nitrogen uptake and transport regulated by potassium,but also give us more clues for uncovering the thorough molecular mechanism.