Biology subjects

Ronald, P. C.

Publications and source records attributed to Ronald, P. C..

4 recordsLinked to original sources

bioRxiv2018

Sulfated RaxX, which represents an unclassified group of ribosomally synthesized post-translationally modified peptides, binds a host immune receptor

The rice immune receptor XA21 is activated by the sulfated microbial peptide RaxX (required for activation of XA21-mediated immunity X) produced by Xanthomonas oryzae pv. oryzae (Xoo). Mutational studies and targeted proteomics revealed that RaxX is processed and secreted by the protease/transporter RaxB, whose function can be partially fulfilled by a noncognate peptidase-containing transporter B (PctB). RaxX is cleaved at a Gly-Gly motif, yielding a mature peptide that retains the necessary elements for RaxX function as an immunogen and host peptide hormone mimic. These results indicate that RaxX is a founding member of a previously unclassified and understudied group of tyrosine sulfated RiPPs (ribosomally synthesized, post-translationally modified peptides). We further demonstrate that sulfated RaxX directly binds XA21 with high affinity. This work reveals a complete, previously uncharacterized biological process: bacterial RiPP biosynthesis, secretion, binding to a eukaryotic receptor and triggering of a robust host immune response.

microbiology↗

bioRxiv2018

A histidine kinase gene is required for large radius root tip circumnutation and surface exploration in rice

The intricate growth patterns that accompany plant organ elongation have long intrigued biologists 1. Circumnutation refers to the circular or elliptical growth of the tip of a plant organ around a central axis. While the utility of circumnutation for climbing plants is clear, its function in roots is less obvious. Additionally, the genetic requirements for root circumnutation are not known. Here we show that mutations in a gene encoding a histidine kinase abolish large radius root tip circumnutation in rice. Using a gel-based imaging system and a whole genome sequenced mutant population, we identified three different mutant alleles of the gene OsHK1 that exhibit increased seedling root depth. Time-lapse imaging indicated that this phenotype is likely due to a lack of large radius root tip circumnutation in OsHK1 mutants. Treatment of mutant roots with the plant hormone zeatin rescues circumnutation, indicating that OsHK1 functions in a cytokinin-related signaling pathway. We found that OsHK1 mutants are impaired in their ability to explore flat surfaces, suggesting that circumnutation facilitates root exploration at the interface of compacted soil horizons.

plant biology↗

bioRxiv2017

A microbially derived tyrosine sulfated peptide mimics a plant peptide hormone

O_LIThe biotrophic pathogen Xanthomonas oryzae pv. oryzae (Xoo) produces a sulfated peptide named RaxX, which shares similarity to peptides in the PSY (plant peptide containing sulfated tyrosine) family. We hypothesize that RaxX functionally mimics the growth stimulating activity of PSY peptides.\nC_LIO_LIRoot length was measured in Arabidopsis and rice treated with synthetic RaxX peptides. We also used comparative genomic analysis and Reactive Oxygen Species (ROS) burst assay to evaluate the activity of RaxX and PSY peptides.\nC_LIO_LIHere we found that a synthetic sulfated RaxX derivative comprising 13 residues (RaxX13-sY), highly conserved between RaxX and PSY, induces root growth in Arabidopsis and rice in a manner similar to that triggered by PSY. We identified residues that are required for activation of immunity mediated by the rice XA21 receptor but that are not essential for root growth induced by PSY. Finally, we showed that a Xanthomonas strain lacking raxX is impaired in virulence.\nC_LIO_LIThese findings suggest that RaxX serves as a molecular mimic of PSY peptides to facilitate Xoo infection and that XA21 has evolved the ability to recognize and respond specifically to the microbial form of the peptide.\nC_LI

plant biology↗

bioRxiv2017

The Sequence of 1504 Mutants in the Model Rice Variety Kitaake Facilitates Rapid Functional Genomic Studies

The availability of a whole-genome sequenced mutant population and the cataloging of mutations of each line at a single-nucleotide resolution facilitates functional genomic analysis. To this end, we generated and sequenced a fast-neutron-induced mutant population in the model rice cultivar Kitaake (Oryza sativa L. ssp. japonica), which completes its life cycle in 9 weeks. We sequenced 1,504 mutant lines at 45-fold coverage and identified 91,513 mutations affecting 32,307 genes, 58% of all rice genes. We detected an average of 61 mutations per line. Mutation types include single base substitutions, deletions, insertions, inversions, translocations, and tandem duplications. We observed a high proportion of loss-of-function mutations. Using this mutant population, we identified an inversion affecting a single gene as the causative mutation for the short-grain phenotype in one mutant line with a small segregating population. This result reveals the usefulness of the resource for efficient identification of genes conferring specific phenotypes. To facilitate public access to this genetic resource, we established an open access database called KitBase that provides access to sequence data and seed stocks, enabling rapid functional genomic studies of rice.\n\nOne-sentence summaryWe have sequenced 1,504 mutant lines generated in the short life cycle rice variety Kitaake (9 weeks) and established a publicly available database, enabling rapid functional genomic studies of rice.

plant biology↗