Molecular Mechanism Of Rice CBL1 Involved In Nitrate Regulated Root Development

Root system is an important organ of plants.It has many physiological functions,such as:Fixing plants,absorbing nutrients and water,composing and storing nutrients.Plants extend its position and area on the earth by growing lateral roots and little roots.The growth state of root system decides its capacity of utilizing nutrients.The growth and morphological configuration of plant roots are not only regulated by self-developmental signals,but also closely related to nutrients in the environment.There are complex interactions between them.Nitrogen nutrition is essential for plant growth and is usually absorbed from the soil by plants in the form of NO₃^-or NH₄⁺.It is known that NO₃^-not only acts as a nutrient component,but also acts as a signaling molecule regulating root growth.Plants can regulate its growth according to the changes of exterior concentration of NO₃^-.This research uses the rice root system of CBL1 Knock-Down to study the role of CBL1-mediated calcium signaling in root system growth and nitrate signaling transmission.The results are as follows:1.Nitrate had different regulating mode of growth and development towards different rice root system.In the MS medium deprived of NH₄⁺,NO₃^-,K⁺,PO₄^2-,the growth status of different roots of rice varied greatly,indicating that different nutrient elements have different regulation modes of growth and development for roots.Cultivate the WT and cbl1-KD plants with 0 m M,0.2 m M,0.5 m M,1 m M,2 m M nitrate solution for 7 days,there is no difference between the primary roots.On the other hand,under the condition of nitrate,the difference between cbl1-KD and the WT plants in the number of crown roots,total length of roots and lateral root length decreased,and the increase of crown root growth rate and lateral root growth rate only occurred in low concentration nitrate culture conditions.2.The expression of Os CBL1 of rice varied in different root system.The fusion expression vector of Os CBL1 promoter and GUS was constructed.Fluorescence quantification and GUS tissue chromosome showed that Os CBL1 was expressed in different growth stages of crown root and lateral root,but the expression level in the primary root was very weak.The Real-Time results of MADS gene family genes showed that under nitrate treatment conditions,the expression trends of WT and cbl1-KD plant primary roots were the same,while the expression trends of both in the crown roots were opposite.3.Os CBL1 changed the auxin composition of rice crown root and lateral root under the nitrate cultivation conditions.Under nitrate cultivation condition,the expression of auxin synthesis genes like Tar5,YUCCA3,YUCCA4,YUCCA6,YUCCA9in cbl1-KD crown root decreased,but the expression trends of genes related to auxin in primary root were without any laws.A fusion expression vector of DR5 and GUS was constructed to analyze the auxin signal in rice roots.It was found that low concentration（0.2 mm）of nitrate cultivation can alleviate the difference between auxin signal of KD and WT plants in lateral root growth and development.However,this phenomenon does not occur in high concentration（2 m M）nitrate cultivation.4.Os CBL1 is involved in the induction of nitrate in rice roots rather than transport.The nitrate content of the primary root and crown root of WT and KD plants were not significantly different under different nitrate concentration conditions.There was no difference in the transport capacity of nitrate by Na¹⁵NO₃.Analysis of gene expression with the original nitrate reaction showed that the response of cbl1-KD plants to low-concentration nitrate treatment was weak compared to the WT plants.The response to high-concentration nitrate treatment became more intense,and root-separation experiments also found that the capacity of lateral roots response to nitrate became weak.5.Os CBL1 can raise the nitrogen utilization of efficiency of rice under low nitrogen conditions.Field experiments showed that compared with WT plants,there were little difference in the rice seed-setting rate,1000-grain weight and yield per plant of cbl1-KD plants in the low nitrogen soil environment,and the effective rice ears exceeded the WT;However,the seed-setting rate,1000-grain weight and yield per plant were significantly reduced compared with WT plants under the high nitrogen conditions.