Plasmodiophora brassicae causes clubroot, a major disease of Brassica oil and vegetable crops worldwide. P. brassicae is a Plasmodiophorid, obligate biotrophic protist in the eukaryotic kingdom of Rhizaria. Here we present the 25.5 Mb genome draft of P. brassicae, developmental stage-specific transcriptomes and a transcriptome of Spongospora subterranea, the Plasmodiophorid causing powdery scab on potato. Like other biotrophic pathogens both Plasmodiophorids are reduced in metabolic pathways. Phytohormones contribute to the gall phenotypes of infected roots. We report a protein (PbGH3) that can modify auxin and jasmonic acid. Plasmodiophorids contain chitin in cell walls of the resilient resting spores. If recognized, chitin can trigger defense responses in plants. Interestingly, chitin-related enzymes of Plasmodiophorids built specific families and the carbohydrate/chitin binding (CBM18) domain is enriched in the Plasmodiophorid secretome. Plasmodiophorids chitin synthases belong to two families, which were present before the split of the eukaryotic Stramenopiles/Alveolates/Rhizaria/Plantae and Metazoa/Fungi/Amoebozoa megagroups, suggesting chitin synthesis to be an ancient feature of eukaryotes. This exemplifies the importance of genomic data from unexplored eukaryotic groups, such as the Plasmodiophorids, to decipher evolutionary relationships and gene diversification of early eukaryotes.

Root induction by auxins is still not well understood at the molecular level. In this study a system has been devised which distinguishes between the two active auxins indole-3-butyric acid (IBA) and indole-3-acetic acid (IAA). IBA, but not IAA, efficiently induced adventitious rooting in Arabidopsis stem segments at a concentration of 10 μM. In wild-type plants, roots formed exclusively out of calli at the basal end of the segments. Root formation was inhibited by 10 μM 3,4,5-triiodobenzoic acid (TIBA), an inhibitor of polar auxin transport. At intermediate IBA concentrations (3–10 μM), root induction was less efficient in trp1, a tryptophan auxotroph of Arabidopsis with a bushy phenotype but no demonstrable reduction in IAA levels. By contrast, two mutants of Arabidopsis with measurably higher levels of IAA (trp2, amt1) show root induction characteristics very similar to the wild type. Using differential display, transcripts specific to the rooting process were identified by devising a protocol that distinguished between callus production only and callus production followed by root initiation. One fragment was identical to the sequence of a putative regulatory subunit B of protein phosphatase 2A. It is suggested that adventitious rooting in Arabidopsis stem segments is due to an interaction between endogenous IAA and exogenous IBA. In stem explants, residual endogenous IAA is transported to the basal end of each segment, thereby inducing root formation. In stem segments in which the polar auxin transport is inhibited by TIBA, root formation does not occur.

In plants, UGTs (UDP-glycosyltransferases) glycosylate various phytohormones and metabolites in response to biotic and abiotic stresses. Little is known about stress-responsive glycosyltransferases in plants. Therefore, it is important to understand the genomic and transcriptomic portfolio of plants with regard to biotic and abiotic stresses. Here, we identified 140, 154, and 251 putative UGTs in Brassica rapa, Brassica oleracea, and Brassica napus, respectively, and clustered them into 14 major phylogenetic groups (A–N). Fourteen major KEGG pathways and 24 biological processes were associated with the UGTs, highlighting them as unique modulators against environmental stimuli. Putative UGTs from B. rapa and B. oleracea showed a negative selection pressure and biased gene fractionation pattern during their evolution. Polyploidization increased the intron proportion and number of UGT-containing introns among Brassica. The putative UGTs were preferentially expressed in developing tissues and at the senescence stage. Differential expression of up- and down-regulated UGTs in response to phytohormone treatments, pathogen responsiveness and abiotic stresses, inferred from microarray and RNA-Seq data in Arabidopsis and Brassica broaden the glycosylation impact at the molecular level. This study identifies unique candidate UGTs for the manipulation of biotic and abiotic stress pathways in Brassica and Arabidopsis.

Reduced unloading and enhanced loading of sulfate increased xylem sap sulfate during early drought, which affects the opening of the ALMT12 channel and induces