Tumour development in Arabidopsis thaliana involves the Shaker‐like K+ channels AKT1 and AKT2/3

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Abstract
After completion of the Arabidopsis genome‐sequencing programme, crown galls induced by Agrobacterium tumefaciens may become a model system to study plant tumour development. The molecular mechanisms of nutrient supply to support tumour growth and development are still unknown. In this study, we have identified a unique profile of Shaker‐like potassium channels in agrobacteria‐induced Arabidopsis tumours. Comparing the gene expression pattern of rapidly growing tumours with that of non‐infected tissues, we found the suppression of shoot in favour of root‐specific K+ channels. Among these, the upregulation of AKT1 and AtKC1 and the suppression of AKT2/3 and GORK were most pronounced. As a consequence, K+ uptake and accumulation were elevated in the tumour (163 mm) compared to control tissues (92 mm). Patch clamp studies on tumour protoplasts identified a population expressing the electrical properties of the AKT1 K+ channel. Furthermore, plants lacking a functional AKT1 or the AKT2/3 phloem K+ channel gene did not support tumour growth. This indicates that the delivery of potassium by AKT1 and the direction of assimilates, triggered by AKT2/3, are essential for tumour growth.