Molecular Mechanism By Which Apple Red-Flesh Locus MdMYB10 Regulates Nitrate Uptake And Allocation

Nitrogen,the most abundant element which is essential for plant growth and development,is main component of fundamental biological macromolecules,such as nucleotides,amino acids,proteins and phospholipids.For most of higher plants especially terrestrial plants,nitrate is the major nitrogen source.Nitrate not only acts as a nutrient,but also acts as a signal molecular to regulate growth and development of plants.With the rapid development of social economy and agricultural production,chemical fertilizer,especially nitrogen fertilizer becomes an indispensable means of agriculture.However excessive fertilization not only increases the cost of agricultural production and waste of resources,but also causes the environmental degradation of soil and water pollution,affecting the agricultural sustainable development and the quality and safety of agricultural products.Therefore,in order to reduce the consumption of nitrogen fertilizer,and increase nitrogen utilization efficiency(NUE)in plants,the study and understanding of how plants take up,transport,assimilate,store,and redistribute nitrogen has very important significance.The nitrate uptake by the root from the soil and the intercellular and intracellular movement of nitrate inside the plant is mediated by the membrane-bound nitrate transporters.In higher plants,nitrate transporter 1/peptide transporter(NRT1/PTR),nitrate transporter 2(NRT2),chloride channel(CLC),and slow anion channel associated 1 homolog 3(SLAC1/SLAH),are involved in the uptake,transportion,storage and redistribution of nitrate.Most of the nitrate uptaked by the root needed to be reduced to be used,and only a small fraction of it is stored in the vacuole as ion balance and osmotic regulation substance.The molecular mechanisms of nitrate uptake,allocation and assimilation have been intensively researched and proved,and however,the regulatory mechanisms are known little.In this study,the red flesh apple,which coloration is determined by Md MYB10 TF,is identified with high nitrate uptake efficiency.First,the red flesh apples and the red flesh of the red hybrid population separation offspring could improve nitrate uptake efficiency.At the same time,in the low concentration of nitrate(0.5 mM)condition,MdMYB10 transgenic apple calli and red flesh apple seedings could also improve nitrate uptake efficiency.Subsequently,RNA-seq analysis was carried out in the red hybrid population separation offspring.And as a result,in the red-leaf apple seeding,the expression levels of MdNRT2 s and MdNIAs genes were enhanced.The in vitro and in vivo experiments showed that MdMYB10 TF could directly bind to the promoter of the high affinity nitrate transporter MdNRT2.4-1 gene,and then activated its expression.Therefore in a low concentration of nitrate(0.5 mM)condition,MdMYB10 TF could improve nitrate uptake efficiency partially through Md NRT2.4-1.Meanwhile,the results indicated that in low concentration of nitrate(0.5 mM)condition,MdMYB10 TF regulated nitrate reallocation from old to young leaves through MdNRT2.4-1 to improve nitrate uptake efficiency.Finally,our findings provided a novel insight into the mechanism by which MYB TF could control nitrate uptake and allocation in apple as well as in other plants in order to make the plants adapt to different nitrogen environment.