Bellenot, C. | Search bioRxiv

bioRxiv2023

A fully sequenced collection of homozygous EMS mutants for forward and reverse genetic screens in Arabidopsis thaliana

Genetic screens are powerful tools for biological research and are one of the reasons for the success of the thale cress Arabidopsis thaliana as a model species. Here, we describe the whole-genome sequencing of 871 Arabidopsis lines from the Homozygous EMS Mutant (HEM) collection as a novel resource for forward and reverse genetics. With an average 576 high-confidence mutations per HEM line, over three independent mutations altering protein sequence are found on average per gene in the collection. Pilot reverse genetics experiments on reproductive, developmental and physiological traits confirmed the efficacy of the tool for identifying both null and knockdown alleles. The possibility of conducting subtle repeated phenotyping of HEM lines and the immediate availability of the mutations will empower forward genetic approaches. The sequence resource is searchable with the ATHEM web interface (https://lipm-browsers.toulouse.inra.fr/pub/ATHEM/), and the biological material is distributed by the Versailles Arabidopsis Stock Center.

plant biology↗

bioRxiv2022

Arabidopsis hydathodes are sites of intense auxin metabolism and nutrient scavenging

Hydathodes are small organs located on the leaf margins of all vascular plants. They release excess xylem sap through guttation when stomata are closed or when the humidity level is high. Many promoter analyses have suggested other hydathode functions in metabolite transport and auxin metabolism, but experimental demonstration is still lacking. Here, we compared the transcriptomic and metabolomic features of mature Arabidopsis hydathodes to the leaf blade. 1460 differentially-expressed genes were identified revealing that genes related to auxin metabolism, transport, stress, DNA, plant cell wall, RNA or wax were on average more expressed in hydathodes. On the other hand, genes involved in glucosinolate metabolism, sulfation pathway, metal handling or photosynthesis were downregulated in hydathodes. In hydathodes, there are an increased expression of auxin transcriptional regulators and biosynthetic genes, a lower expression of auxin transport genes and a differential expression of genes related to its vacuolar storage that is consistent with increased contents of free and conjugated auxin. We also found that ca. 78% of the total content of 52 xylem sap metabolites were removed from guttation fluid at the hydathode level. Using reverse genetics, we showed that the capture of nitrate and phosphate in the guttation fluid relies on the NRT2.1 and PHT1;4 transporters, respectively. Thus, hydathodes absorb a significant part of xylem sap nutrients, limiting the loss of valuable chemicals during guttation. Our transcriptomic and metabolomic analyses reveal an organ with its own transcriptomic and physiological identity and highlight hydathode biological processes that may impact the whole plant. One sentence summaryTranscriptome and physiological analysis of mature and healthy hydathodes of Arabidopsis demonstrates that those organs are sites of intense auxin metabolism and nutrient scavenging

plant biology↗