Aromatic amino acid biosynthesis by a Lotus Aldolase impacts root hair development and symbiotic associations

Abstract

O_LILegume roots can be symbiotically colonized by arbuscular mycorrhizal (AM) fungi and nitrogen-fixing bacteria. In Lotus japonicus, the latter occurs intracellularly by the cognate rhizobial partner Mesorhizobium loti or intercellularly with the Agrobacterium pusense IRBG74 strain. Although these symbiotic programs show distinctive cellular and transcriptome signatures, some molecular components are shared. C_LIO_LIIn this study, we demonstrate that Aldolase1, the first enzyme in the biosynthetic pathway of aromatic amino acids (AAA), plays a critical role in root hair development and for AM and rhizobial symbioses in Lotus. C_LIO_LITwo homozygous mutants affected in Aldolase1 (ald1-1 and ald1-2) show drastic alterations in the root hair morphology, associated with a progressive disruption of the actin cytoskeleton. The altered root hair structure was prevented by chemical and genetic complementation. C_LIO_LIBoth ald1-1 and ald1-2 show significant reductions in rhizobial infection (intracellular and intercellular), nodule organogenesis and AM colonization. RNAseq analysis of ald1-2 roots suggested that these phenotypes are associated with downregulation of several cell wall related genes, and with an attenuated symbiotic signalling. This work provides robust evidence that links AAA metabolism to root hair development and successful symbiotic associations. C_LI