Expression of KT/KUP genes in Arabidopsis and the role of root hairs in K+ uptake.
Potassium (K(+)) is the most abundant cation in plants and is required for plant growth. To ensure an adequate supply of K(+), plants have multiple mechanisms for uptake and translocation. However, relatively little is known about the physiological role of proteins encoded by a family of 13 genes, named AtKT/KUP, that are involved in K(+) transport and translocation. To begin to understand where and under what conditions these transporters function, we used reverse transcription-PCR to determine the spatial and temporal expression patterns of each AtKT/KUP gene across a range of organs and tested whether selected AtKT/KUP cDNAs function as K(+) transporters in Escherichia coli. Many AtKT/KUPs were expressed in roots, leaves, siliques, and flowers of plants grown under K(+)-sufficient conditions (1.75 mm KCl) in hydroponic culture. AtHAK5 was the only gene in this family that was up-regulated upon K(+) deprivation and rapidly down-regulated with resupply of K(+). Ten AtKT/KUPs were expressed in root hairs, but only five were expressed in root tip cells. This suggests an important role for root hairs in K(+) uptake. The growth and rubidium (Rb(+)) uptake of two root hair mutants, trh1-1 (tiny root hairs) and rhd6 (root hair defective), were studied to determine the contribution of root hairs to whole-plant K(+) status. Whole-plant biomass decreased in the root hair mutants only when K(+) concentrations were low; Rb(+) (used as a tracer for K(+)) uptake rates were lower in the mutants at all Rb(+) concentrations. Seven genes encoding AtKUP transporters were expressed in E. coli (AtKT3/KUP4, AtKT/KUP5, AtKT/KUP6, AtKT/KUP7, AtKT/KUP10, AtKT/KUP11, and AtHAK5), and their K(+) transport function was demonstrated.
Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, Missouri 63132, USA.
Sung Ju
SJ
Ahn
Ryoung
R
Shin
Daniel P
DP
Schachtman
D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D018744:DNA, Plant / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005091:Exons; D015870:Gene Expression; D017343:Genes, Plant; D005816:Genetic Complementation Test; D007438:Introns; D017136:Ion Transport; D018517:Plant Roots / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism
D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D018744:DNA, Plant; D012333:RNA, Messenger; D018749:RNA, Plant; D011994:Recombinant Proteins; D012413:Rubidium; D011188:Potassium