MeCIPK23-MeAKT1-Mediated Plant Response To Low Potassium Stress In Cassava

Potassium(K)participates in many important physiological processes of plants,it is indispensable in plant growth and development and the whole life cycle.Potassium ion(K+)is mainly absorbed by plants through K+transporters and K+protein channels,and transported or distributed in plants.It is one of the most abundant cations in plants.Cassava is one of the most important food crops in the world.Its tuberous root is rich in starch,which has a wide range of edible and industrial value.Potassium deficiency in soil is an important factor to decrease cassava yield.Therefore,it is of great significance to breed cassava varieties resistant to low potassium and increase cassava yield by exploring the related genes and the molecular mechanism of cassava response to low potassium stress.As an important component of potassium protein channel,Arabidopsis thaliana K+transporter 1(AKT1)mediates the absorption of potassium by roots.However,AKT1 gene has not been cloned in cassava.In this study,the expression of AKT1 gene in cassava was detected by Real-time quantitative polymerase chain reaction(qT-PCR)after low potassium treatment,it was found that the expression of AKT1 gene increased significantly.It was speculated that AKT1 gene played a role in the response of cassava to low potassium stress.Subsequently,the physiological functions of AKT1 protein channel and the CBL-CIPKAKT1 pathway formed by calcineurin B-like protein 1/9(CBL1/9)and CBL-interacting protein kinase 23(CIPK23)were studied to regulate the molecular mechanism of cassava resistance to low potassium stress,so as to provide a theoretical basis for the cultivation of cassava germplasm resources with high potassium nutrition efficiency in the future.The main results are as follows:1.The results showed that the sequence similarity between cassava AKT1 and Arabidopsis AKT1 was high,and it was predicted that they might have similar physiological functions.The transformation of cassava AKT1 gene into K+-absorbing defective yeast strains could partially restore the K+absorption capacity of yeast strains on low potassium medium,indicating that cassava AKT1 gene has K+transport activity.2.The interaction between the cassava AKT1 and CIPK23 was verified by Pull-down assay(Pull down),Co-Immunoprecipitation(CoIP)and Bimolecular fluorescence complementation(BiFC).It was suggested that cassava AKT1 and CIPK23 might play a role in the joint regulation of cassava response to low potassium stress.3.The function of cassava CBL1/9,AKT1 and CIPK23 in the response to low potassium stress was studied by gene silencing system.After the expression of these genes was inhibited,cassava plants showed more obvious low potassium sensitive phenotype under low potassium stress,and the more kinds of genes were inhibited,the low potassium tolerance of cassava plants was weaker.4.The overexpression transgenic Arabidopsis plants of cassava CBL1/9,AKT1 and CIPK23 were constructed and cultured in the same low potassium environment as wild type Arabidopsis.After two weeks of culture,according to the plant phenotype and chlorophyll content,it could be judged that the transgenic plants were more tolerant to low potassium stress than the wild type.5.Ten different cassava varieties were treated with low potassium,and the expression levels of CBL1/9,AKT1 and CIPK23 in these cassava varieties were detected.It was found that different varieties of cassava had different tolerance to low potassium,and showed inconsistent low potassium phenotype.The expression of these genes also had obvious differences,which indicated that the resistance difference of different varieties of cassava to low potassium stress might be related to the expression differences of CBL1/9,AKT1 and CIPK23,which provided some help for breeding low potassium resistant cassava varieties.In conclusion,AKT1 plays an important role in cassava resistance to low potassium stress,and is regulated by CBL1/9-CIPK23 signaling pathway.CBL1/9,AKT1 and CIPK23 genes can regulate the response of cassava to low potassium stress,and their overexpression can promote the absorption of K+in cassava under low potassium environment.These results will be helpful to further study the physiological function of AKT1 gene and the role of related genes in CBL-CIPK pathway in cassava resistance to low potassium stress.