The Bacterial Potassium Transporter Gene TrkH Enhances K~+ Nutrition In Transgenic Tobacco And Maize

Potassium is one of the essential nutrients for plant growth and development,and involve in a variety of physiological and biochemical processes,including protein synthesis and photosynthesis.K~+deficiency seriously affects the quality and yield of crop.To improve K~+uptake and utilization efficiency of crop by genetic modification is one of the effective approaches to solve this problem.Studies have shown that overexpression of K~+uptake-related genes improve potassium nutrition in plants,but the transgene are mainly limited to plant sources.Previous studies in our laboratory have found that the bacterial K~+transporter gene trkH can improve the K~+uptake capacity of defective Saccharomyces cerevisiae and the yeast can grow in low-K~+medium.We focused on the overexpression and functional analysis of trkH gene in tobacco and maize,which lays the foundation of breeding.The trkH gene was transformed into tobacco by Agrobacterium-mediated leaf disc transformation method.PCR detection results showed that trkH gene was successfully introduced into tobacco plants.RT-PCR results showed that the trkH gene were expressed at the transcriptional level in four lines,and the L1 and L4 lines with relatively high expression level were selected for further physiological analysis.K~+depletion experiment showed that overexpression of trkH gene increased K~+absorption capacity of transgenic tobacco plants.Hydroponic culture assays showed that the fresh weight,dry weight and K~+content of transgenic tobacco plants were significantly higher than WT at 1 mM K~+concentration.The trkH and bar gene were transformed into maize by Agrobacterium-mediated immature embryo infection method.Twenty-one independent baster resistant maize plants were obtained through the co-cultivation and selection process.The PCR detection results of T0plants showed that trkH gene was successfully introduced into maize plants.Bar strip detection indicated that the bar gene was expressed at the protein level.Partial T0 transgenic plants were crossed with the maize backbone inbred line PH6WC and eight hybrid progeny were obtained.Semi-quantitative RT-PCR results showed that trkH gene were expressed at the transcriptional level in eight lines.Herbicide was sprayed at the three-leaf and one-heart stage,and L3,L5 and L7 lines with a ratio close to 1:1 were selected for PCR detection.Chi-square was performed with PCR data and the results indicate that the ratio is in accordance with Mendelian segregation law.The maize K~+depletion experiment showed that the K~+uptake capacity of L3,L5 and L7lines was better than WT.Hydroponic culture experiments showed that the root length of L5and L7 lines were significantly longer than WT,and the plant height of L5 line was higher than WT,and the fresh weight and dry weight of L3,L5 and L7 lines were significantly higher than WT at 1 mM K~+concentration.In consideration of the above results,the L5 line was selected for further agronomic traits analysis in the field.The field trial showed that when the available K~+content was 100,80 and 30 mg/kg,there were no significant difference in the plant height,ear diameter,row number and ear weight of transgenic maize and WT.When the available K~+content was 80 and 30 mg/kg,transgenic maize plants grew better than WT.When the available K~+content was 30 mg/kg,the ear position and 100-grain weight of transgenic maize were significantly higher than WT.In conclusion,the overexpression bacterial potassium transporter gene trkH provides a new strategy for improving plant potassium absorption.