Mechanism Of Fusaric Acid Inhibiting Banana Cells' Absorption Of Potassium Ions

The outbreak and large-scale epidemics of Foc TR4?Fusarium oxysporum f.sp.cubense tropical race 4?has a strong impact on the world banana industry,posing a direct threat to the economy in tropical and subtropical regions,even to the world food security.Banana is a typical potassium-loving crop,and potassium is necessary for its resistance to the pathogens.High concentration of K⁺ in cytoplasm can limit the growth and infection of the fungal pathogens.Our previous studies have found that fusaric acid?FSA?secreted by Foc TR4 can inhibit the absorption of K⁺ of banana cells.To unravel this mechanism,we investigate the effects of potassium on the growth and development of Foc TR4,the effects of FSA on the accumulation of K⁺ in banana roots and the interaction between FSA and K⁺ channel protein Ma AKT1.The results are as follows:?1?Morphological relationship between Fusarium wilt of banana and the symptoms of potassium deficiency: Comparative analysis results showed that symptoms of potassium deficiency are one part of the external symptoms of Foc TR4-infection.The lower leaves and the outer leaf sheath first showed specific yellowing at the leaf edge,and then spreading to the midrib one by one,which is remarkable compared with the dark green part of the leaves;Fruit were stunted with poor quality;FSA secreted by Foc TR4 can make banana plants yellowing withreduced potassium content,presenting symptoms of potassium deficiency,suggesting that FSA is an important virulence factor in Foc TR4 by causing potassium deficiency in banana plants.?2?Potassium concentration is directly related to the growth and development of Foc TR4: Foc TR4 strains were treated with different concentrations of KCl and KNO₃,and it was found that when there was no potassium in the basic medium,Foc TR4 grew slowly;when the concentration of 1-4 mmol·L^-1 K⁺ were added to the MM medium,Foc TR4 grows vigorously.When the concentration is higher than 5 mmol·L^-1 K⁺,the growth of Foc TR4 strain obviously begins to be inhibited;the K⁺ concentration in plant cytoplasm can be maintained between 100-200 mmol·L^-1,presumably reducing intracellular potassium concentration is one of the strategies for Foc TR4 to infect banana successfully.?3?FSA significantly inhibited the accumulation of potassium in banana cells and root tissues: Adding 20 ?mol·L^-1 FSA and gradient concentration K⁺ to the protoplast of Baxi banana suspension showed that FSA could significantly inhibit the absorption of K⁺ in banana cells.In both normal-cultivated and potassium-deficient-cultivated banana tissue culture seedlings,20 ?mol·L^-1 FSA significantly inhibited the uptake and accumulation of K⁺ in roots.Meanwhile,it was found that FSA could reduce the enzyme activity of reactive oxygen metabolic enzymes and defense-related hydrolase.?4?Overexpression of Ma AKT1: the previous RNA-seq and q RT-PCR experiments demonstrated that Ma AKT1 was the sinificantly affected K⁺channel protein gene by FSA.Computer simulation of molecular docking predicts that the N atom in the pyridine ring of FSA can interact with the 648 th glycine of the Ma AKT1 protein through hydrogen bonding.The Ma AKT1 overexpression vector was constructed and transformed into the susceptible banana Baxi and the model plant Arabidopsis thaliana.Plant phenotypic analysis showed that Ma AKT1 could promote the vegetative growth of the plants,and the resistance of transgenic Arabidopsis thaliana to 20 ?mol·L^-1 FSA was significantly enhanced.The resistance of transgenic bananas is being evaluated.