Biology subjects

Sandal, N.

Publications and source records attributed to Sandal, N..

5 recordsLinked to original sources

bioRxiv2025

The Lotus japonicus alpha Expansin EXPA1 is recruited during intracellular and intercellular rhizobial colonization

Most legumes establish a mutualistic association with rhizobia, a group of nitrogen-fixing bacteria. In Lotus japonicus, the symbiotic colonization occurs intracellularly, via root-hair infection threads by Mesorhizobium loti, or intercellularly, with Agrobacterium pusense IRBG74. In both mechanisms, cell wall remodeling is presumably an essential process. In plants, alpha-Expansins (EXPA) promote cell wall loosening by non-enzymatically triggering a pH-dependent relaxation. In this study, we show that LjEXPA1, is critical for the intracellular and intercellular symbiotic program in L. japonicus. Promoter activity and subcellular localization analyses revealed that EXPA1 is recruited at essential compartments and structures of epidermal and cortical cells in both mechanisms of rhizobial infection, such as the infection chambers, infection pockets and transcellular infection threads. Additionally, EXPA1-YFP abundantly accumulated in dividing cortical cells during nodule formation. The expression profile of EXPA1 correlates with the symbiotic phenotype observed in homozygous mutants disrupted in the EXPA1 gene (expA1-1 and expA1-2). Infection thread formation and intercellular colonization was drastically reduced in expA1-1 and expA1-2 mutants, respect to wild type plants. Similarly, nodule formation was significantly reduced in these mutants after M. loti or IRBG74 inoculation. Our results indicate that non-enzymatic cell wall remodeling by the alpha Expansin EXPA1 is crucial for the successful establishment of Lotus-rhizobia symbiosis, regardless of the infection mechanism.

plant biology↗

bioRxiv2021

A promiscuity locus confers Lotus burttii nodulation with rhizobia from five different genera

Legumes acquire access to atmospheric nitrogen through nitrogen fixation by rhizobia in root nodules. Rhizobia are soil dwelling organisms and there is a tremendous diversity of rhizobial species in different habitats. From the legume perspective, host range is a compromise between the ability to colonize new habitats, where the preferred symbiotic partner may be absent, and guarding against infection by suboptimal nitrogen fixers. Here, we investigate natural variation in rhizobial host range across Lotus species. We find that Lotus burttii is considerably more promiscuous than Lotus japonicus, represented by the Gifu accession, in its interactions with rhizobia. This promiscuity allows Lotus burttii to form nodules with Mesorhizobium, Rhizobium, Sinorhizobium, Bradyrhizobium, and Allorhizobium species that represent five distinct genera. Using recombinant inbred lines, we have mapped the Gifu/burttii promiscuity QTL to the same genetic locus regardless of rhizobial genus, suggesting a general genetic mechanism for host-range expansion. The Gifu/burttii QTL now provides an opportunity for genetic and mechanistic understanding of promiscuous legume-rhizobia interactions.

plant biology↗

bioRxiv2020

A chromosome-scale Lotus japonicus Gifu genome assembly indicates that symbiotic islands are not general features of legume genomes

AimLotus japonicus is a herbaceous perennial legume that has been used extensively as a genetically tractable model system for deciphering the molecular genetics of symbiotic nitrogen fixation. Our aim is to improve the L. japonicus reference genome sequence, which has so far been based on Sanger and Illumina sequencing reads from the L. japonicus accession MG-20 and contained a large fraction of unanchored contigs. Methods and ResultsHere, we use long PacBio reads from L. japonicus Gifu combined with Hi-C data and new high-density genetic maps to generate a high-quality chromosome-scale reference genome assembly for L. japonicus. The assembly comprises 554 megabases of which 549 were assigned to six pseudomolecules that appear complete with telomeric repeats at their extremes and large centromeric regions with low gene density. Conclusion and PerspectivesThe new L. japonicus Gifu reference genome and associated expression data represent valuable resources for legume functional and comparative genomics. Here, we provide a first example by showing that the symbiotic islands recently described in Medicago truncatula do not appear to be conserved in L. japonicus.

genomics↗

bioRxiv2020

Natural variation identifies a Pxy gene controlling root vascular organization and formation of nodules and lateral roots in Lotus japonicus

Forward and reverse genetics using the model legumes Lotus japonicus and Medicago truncatula have been instrumental for identifying the essential genes governing legume-rhizobial symbiosis. However, little is known about the effects of intraspecific variation on symbiotic signaling. The Lotus accessions Gifu and MG20 show differentiated phenotypic responses to the Mesorhizobium loti exoU mutant that produces truncated exopolysaccharides. Using Quantitative Trait Locus sequencing (QTL-seq), we identify the Pxy gene as a component of this differential exoU response. Lotus Pxy encodes a leucine-rich-repeat kinase similar to Arabidopsis PXY, which regulates stem vascular development. We show that Lotus pxy insertion mutants display defects in root vascular organization, as well as lateral root and nodule formation. Our work links Pxy to de novo organogenesis in the root, highlights the genetic overlap between regulation of lateral root and nodule formation, and demonstrates that specific natural variants of Pxy differentially affect nodulation signaling.

plant biology↗

bioRxiv2018

Extreme genetic signatures of local adaptation during plant colonization

Colonization of new habitats is expected to require genetic adaptations to overcome environmental challenges. Here we use full genome re-sequencing and extensive common garden experiments to investigate demographic and selective processes associated with the recent colonization of Japan by Lotus japonicus. We carefully track the colonization process where L. japonicus gradually spread from subtropical conditions to much colder climates in northern Japan. We characterize the loss of diversity during this process and identify genomic regions with extreme genetic differentiation. Next, we perform population structure-corrected association mapping of phenotypic traits measured in a common garden and discover a number of genome-wide significant associations. Contrasting these analyses, we find that there is a strong concordance between phenotypic variation and extreme differentiation for overwintering and flowering time traits. Our results provide evidence that these traits were direct targets of selection by local adaptation during the colonization process and point to associated candidate genes.

evolutionary biology↗