Redundancies in low K signaling of neo-tetraploids leads in increased shoot K [RNA-seq_2]

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. Overall design: RNAseq of Arabidopsis thaliana wild type Col-0 and mutants esb1-1, sos3-2 and rhd6-3/rsl1-1 after whole genome duplication, grown on soil and plates. Roots and shoots of soil grown plants and roots of plate grown plants were assessed for gene expression differences between diploids and neo-tetraploids. Three replicates were analyed.