Redundancies in low K signaling of neo-tetraploids leads in increased shoot K [RNA-seq_1]

Whole Genome Duplication (WGD) events occurred frequently during land plant evolution and their long term benefits to neo-functionalization of genes and speciation is well known (Baduel et al., 2018). However short term benefits, important for the establishment of a new population, are more difficult to observe until Chao et al., 2013 described a fitness advantage under high salinity. Additionally shoot K levels were higher in neo-tetraploids, an important feature since K uptake becomes increasingly more difficult on highly saline soil. The molecular basis for these phenotypes was not known. Here we analyze neo-tetraploid Arabidopsis thaliana plants using RNAseq and ICP-MS to evaluate the effect of mutations and ploidy on the gene expression and shoot ionome. We are able to show that neo-tetraploid plants induce low-potassium (K) signaling to increase their shoot K content. However, we also show that this low-K signaling is distinct form previously studied, externally applied low-K signaling. In this way, we are able to identify new components of the K homeostasis network, which are required to regulate K demand. Additionally we are able to show that while individual components of the K uptake system are not sufficient to increase shoot K, a loss of root hairs abolished the ploidy K phenotype (PPP) as does a defective Casparian strip. Root hairs are the site of entry of K into the root and neo-tetraploids increase their root hair length and density (RHI) to facilitate their higher K demand. The Casparian strip on the other hand enables higher K concentration in the stele of the root, which is required for the increased K content in neo-tetraploids. RNAseq of Arabidopsis thaliana wild type Col-0 lines after whole genome duplication, under control conditions and salt stress. Roots and shoots of plate grown plants were assessed for gene expression differences between diploids and neo-tetraploids. Three replicates were analyed.