Hummel, S. | Search bioRxiv

bioRxiv2019

AtDAT1 is a key enzyme of D-amino acid stimulated ethylene production in Arabidopsis thaliana

D-enantiomers of proteinogenic amino acids (D-AAs) are found ubiquitously, but the knowledge about their metabolism and functions in plants is scarce. A long forgotten phenomenon in this regard is the D-AA-stimulated ethylene production in plants. As a starting point to investigate this effect the Arabidopsis accession Landsberg erecta (Ler) got into focus as it was found defective in metabolizing D-AAs. Combining genetics and molecular biology of T-DNA lines and natural variants together with biochemical and physiological approaches we could identify AtDAT1 as a major D-AA transaminase in Arabidopsis. Atdat1 loss-of-function mutants and Arabidopsis accessions with defective AtDAT1 alleles were not able to produce D-Ala, D-Glu and L-Met, the metabolites of D-Met, anymore. This result corroborates the biochemical characterization of AtDAT1, which showed highest activity using D-Met as substrate. Germination of seedlings in light and dark led to enhanced growth inhibition of atdat1 mutants on D-Met. Ethylene measurements revealed an enhanced D-AA stimulated ethylene production in these mutants. According to initial working models of this phenomenon D-Met is preferentially malonylated instead of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). This decrease of ACC degradation should then lead to the increase of ethylene production. We could observe in our studies a reciprocal relation of malonylated methionine and ACC upon D-Met application and even significantly more malonyl-methionine in atdat1 mutants. Unexpectedly, the malonyl-ACC levels did not differ between mutants and wild type in these experiments. With AtDAT1, the first central enzyme of plant D-AA metabolism was characterized biochemically and physiologically. The specific effects of D-Met on ACC metabolization, ethylene production and plant development of dat1 mutants unraveled the impact of AtDAT1 on these processes, but they are not in full accordance to previous working models. Instead, our results imply the influence of additional candidate factors or processes on D-AA-stimulated ethylene production which await to be uncovered.

plant biology↗

bioRxiv2019

The striking flower-in-flower phenotype of Arabidopsis thaliana Nossen (No-0) is caused by a novel LEAFY allele

SummaryThe transition to reproduction is a crucial step in the life cycle of any organism. In Arabidopsis thaliana the establishment of reproductive growth can be divided into two phases: In the first phase, cauline leaves with axillary meristems are formed and internode elongation begins. In the second phase, lateral meristems develop into flowers with defined organs. Floral shoots are usually determinate and suppress the development of lateral shoots. Here, we describe a Ds transposon insertion mutant in the Nossen (No-0) accession with severe defects in floral development and flower morphology. The most striking aspect is the outgrowth of stems from the axillary bracts of the primary flower carrying terminal secondary flowers. Therefore, we named this mutant flower-in-flower (fif). However, the insertion of the transposon in the annotated gene is not responsible for the fif phenotype. By means of classical and genome sequencing-based mapping, the mutation responsible for the fif phenotype was found to be in the LEAFY (LFY) gene. The mutation, a G-to-A exchange in the second exon of LFY, creates a novel lfy allele and causes a cysteine-to-tyrosine exchange in the 1-helix of the LFY DNA-binding domain. Whereas subcellular localization and homomerization are not affected, the DNA-binding of LFYFIF is abolished. We propose that the amino acid exchange interferes with the cooperative binding of LFY to its target DNA. To generate the strong fif phenotype, LFYFIF may act dominant-negatively by either forming non-binding LFY/LFYFIF heteromers or by titrating out the interaction partners, required for LFY function as transcription factor. Significant StatementThe fif phenotype of Arabidopsis thaliana No-0 is caused by a novel allele of the LEAFY gene

plant biology↗