Characterization and fine mapping of a potassium dependent growth QTL in Arabidopsis

Potassium is an essential macronutrient for plants. Deficiency in potassium leads to a reduction in organ growth and can cause yield loss. Previously, a quantitative trait locus (QTL) analysis was performed with a Ler/Kas-2 recombinant inbred line (RIL) population of Arabidopsis thaliana that was grown using a hydroponic system with contrasted mineral nutrient supplies. QTL for growth related and biochemical traits were detected in each condition. Furthermore, QTL involved in response of these traits to differences in nutrient supply were also detected. The genetic basis of these response QTL could be involved in the adaptation of the plant to the reduction in mineral nutrient supply. One of these QTL was mapped on the bottom of the chromosome five and was involved in the response of rosette weight to lowered potassium supply. In the present study, this response QTL was validated with near isogenic lines (NILs) that had a Kas-2 introgression only at the QTL position in an otherwise Ler genetic background. The NILs retained over 20% more rosette weight than Ler in response to the reduced potassium supply. The QTL was further characterized: its effect on growth was present in a wide range of reduced potassium supplies but was abolished in the presence of ammonium. Furthermore, the NILs showed generally higher potassium content in the rosette as well as a higher water loss than Ler. There was no difference in stomatal density between the NILs and Ler and it is therefore assumed that a differential regulation of stomata opening will cause the water loss difference. The QTL was fine mapped to a ca 3.9 Mbp region and the response phenotype of different recombinant lines suggested that several interacting genes led to the observed effect of the QTL on growth in response to potassium reduction. The selection of candidate genes, underlying the effect of the QTL, is discussed and amongst others the potassium channel TPK1. Identification of the genetic and molecular basis of this QTL may shed light on a new regulatory mechanism that influences plant growth in response to potassium starvation and confers higher potassium efficiency to plants