Biology subjects

Frommer, W.

Publications and source records attributed to Frommer, W..

8 recordsLinked to original sources

bioRxiv2026

Pyramiding four genes governing bacterial blight resistance in three popular rice varieties of East Africa and Madagascar

Bacterial blight of rice causes substantial crop losses in Asia and Africa. The recent introduction of Asian strains into African countries has led to two independent outbreaks detected in 2019, causing severe damage in Madagascar and Tanzania. The strains are highly virulent on local rice varieties and rapidly spread from Tanzania to neighboring countries. Multiplex genome editing of effector-binding elements in the promoter of SWEET rice promoters has successfully generated elite rice lines with broad-spectrum resistance against bacterial blight. While genome-edited crops can be released in countries with biosafety regulations, their use in countries that have yet to establish regulations, e.g., Tanzania and Madagascar, is hindered. To circumvent this, marker-assisted backcross breeding (MABB) of the African elite varieties Komboka, FARO-44, and NE-RICA-4 was adopted to introgress resistance genes to confer resistance to Xoo strains identified in Tanzania (iTz) and Madagascar (iMg). Resistance gene pyramiding, namely Xa1, Xa4, xa13, and Xa21, in the three elite rice varieties conferred resistance to iTz and iMg strains. Our study presents a solution to provide rice breeders in East Africa with bacterial blight resistance in three local rice varieties for field trials, line registration, and deployment.

Plant Biology↗

bioRxiv2026

Rice bacterial blight resistance in Burkina Faso through genome editing: Evaluating pathogen and agro-morphological compatibility of genome-edited elite rice varieties

Bacterial leaf blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), causes yield losses exceeding 50% in affected areas, including the Bagre rice plain in Burkina Faso. Genome-edited (GEd) rice lines have been successful in tackling BB. Modifications in the Xoo virulence protein target site upstream of three SWEET susceptibility genes in two elite rice varieties, IR64 and Ciherang-Sub1, have been demonstrated to confer broad-spectrum resistance to Asian and East African Xoo strains. Here, we evaluate the potential of the GEd lines as a solution for BB management in Burkina Faso. We challenged the GEd lines against five locally collected Burkinabe Xoo strains under controlled green-house conditions and assessed their agro-morphological performance under field conditions representative of local agroecological conditions. Greenhouse pathogen assays demonstrated that GEd IR64 and Ciherang-Sub1 lines were resistant to all tested local Xoo strains across three successive generations. We identified TalC as the primary disease-causing effector in the local Xoo populations. Irrigated field trials conducted over two seasons in the Kou Valley, Burkina Faso, revealed absence of agro-morphological penalties in GEd lines compared to their parental wild-type lines. Observed trait variation was attributable to environmental fluctuations rather than genomic modifications. Collectively, our findings demonstrate that genome editing of the rice lines does not impose growth penalties, and support the suitability of GEd IR64 and Ciherang-Sub1 for large-scale adoption in Burkina Faso, pending multi-location validation and introgression into locally adapted varieties.

Plant Biology↗

bioRxiv2026

A receptor-like kinase controls plasmodesmal transport of conserved 30K viral movement proteins through phosphorylation

Intercellular viral movement in plants is mediated by movement proteins (MPs) that modulate plasmodesmata (PD) enabling cell-to-cell and systemic trafficking. Although phosphorylation has long been implicated in the regulation of MP localization and activity, the identity of host kinases and the interface with immune signaling have remain unresolved. Here, we identified the Arabidopsis thaliana lectin receptor-like kinase RDA2 as a PD-associated regulatory component of viral movement. Using proximity labeling, we detected RDA2 as a proximal interactor of the tobacco mosaic virus (TMV) MP, and show that RDA2 directly phosphorylates MP at multiple sites in vitro. Phosphorylation at threonine 75 is required for efficient PD targeting and intercellular movement, while phospho-dead mutants failed to complement viral spread. Loss of RDA2 enhanced MP mobility and increased TMV accumulation in planta, indicating that RDA2 modulates PD transport during the infection. RDA2 also interacted with and phosphorylated the movement protein of cucumber mosaic virus, implicating that this regulatory mechanism extends across members of the 30K MP superfamily. Our findings demonstrate that a plasma membrane receptor-like kinase can directly modify viral movement proteins, establishing a mechanistic link between receptor-mediated immune signaling and the post-translational control of symplasmic connectivity. One-sentence summaryRDA2, a lectin receptor-like kinase, directly phosphorylates conserved 30K viral movement proteins to control their plasmodesmal targeting and restrict cell-to-cell viral spread in plants

plant biology↗

bioRxiv2025

Making plant tissue accessible for cryo-electron tomography

Cryo-Electron Tomography (cryo-ET) allows to visualize the molecular architecture of pristinely preserved cells and tissues. The workflow of sample preparation for cryo-ET is rather complex; it involves vitrification by rapid freezing followed by cryo-Focused Ion Beam (FIB) milling rendering the volumes of interest thin enough for cryo-ET data acquisition. The established protocols for single cells grown on or deposited on EM-grids are not suitable for multicellular plant tissues. Plunge-freezing does not yield vitrified samples in most cases and must be replaced by high-pressure freezing. This, in turn, necessitates extensive modifications of the subsequent FIB milling procedures. In this communication we describe procedures for sample screening, targeted FIB milling guided by cryo-fluorescence microscopy and a novel lamella trimming step that allows to obtain homogenously thin lamellae suitable for cryo-ET. We have tested all the steps along the workflow with a variety of plant tissues including the moss Physcomitrium patens and tissues of Arabidopsis thaliana and Limonium bicolor. We could demonstrate that the workflow optimized for plant tissues allows to attain subnanometer resolution in cases where subtomogram averaging is applicable.

plant biology↗

bioRxiv2020

Quantitative analysis of transporter activity biosensors

The allocation of sugars from photosynthetic leaves to storage tissues in seeds, fruits, and tubers is an important determinant of crop yields. Genetically guided selection and transgenic modification of plant membrane transporters can help enhance crop yields and increase pathogen resistance. Yet, quantitative, systems-level models to support this effort are lacking. Recently, biosensors gained popularity for collecting spatiotemporally resolved information on cell physiology and validating computational models. Here, we report the design and use of genetically-encoded biosensors to measure the activity of SWEETs, the only family of sugar transporters known to facilitate the cellular release of sugar in plants. We created SweetTrac sensors by inserting circularly-permutated GFP into SWEET transporters, resulting in chimeras that translate substrate-triggered conformational rearrangements during the transport cycle into detectable changes in fluorescence intensity. We demonstrate that a combination of cell sorting and bioinformatics can be applied as a general approach to accelerate the design of biosensors for in vivo biochemistry. Finally, mass action kinetics analysis of the biosensors response suggests that SWEETs are low-affinity, near-symmetric transporters that can rapidly equilibrate intra- and extracellular concentrations of sugars. Significance StatementTransporters are the gatekeepers of the cell. Transporters facilitate the exchange of ions and metabolites between cellular and subcellular compartments, thus controlling processes from bacterial chemotaxis to the release of neurotransmitters. In plants, transporters play critical roles in the allocation of carbon to different organs. Biosensors derived from transporters have been generated to monitor the activity of these proteins within the complex environment of the cell. However, a quantitative framework that reconciles molecular and cellular-level events to help interpret the response of biosensors is still lacking. Here, we created novel sugar transport biosensors and formulated a mathematical model to explain their response. These types of models can help realize multiscale, dynamic simulations of metabolite allocation to guide crop improvement.

bioengineering↗

bioRxiv2017

SWEET11 and 15 as key players in seed filling in rice

SummaryO_LIDespite the relevance of seed filling mechanisms for crop yield, we still have only a rudimentary understanding of the pathways and transport processes for supplying the caryopsis with sugars. We hypothesized that the recently identified SWEET sucrose transporters may play important roles in nutrient import pathways in the rice caryopsis.\nC_LIO_LIWe used a combination of mRNA quantification, histochemical analyses, translational promoter-reporter fusions and analysis of knock out mutants created by genomic editing to evaluate the contribution of SWEET transporters to seed filling.\nC_LIO_LIIn rice caryopses, SWEET11 and 15 had the highest mRNA levels and proteins localized to four key sites: the nucellus proper at early stages, the nucellar projection close to the dorsal vein, the nucellar epidermis that surrounds the endosperm, and the aleurone. ossweet11;15 double knock-out lines accumulated starch in the pericarp while caryopses did not contain a functional endosperm.\nC_LIO_LIJointly, SWEET11 and 15 show all hallmarks of being responsible for seed filling with sucrose efflux function at the nucellar projection and transfer across the nucellar epidermis/aleurone interface, delineating two major steps for apoplasmic seed filling, observations that are discussed in relation to observations made in rice and barely on the relative prevalence of these two potential import routes.\nC_LI

plant biology↗

bioRxiv2017

Impaired phloem loading in genome-edited triple knock-out mutants of SWEET13 sucrose transporters

Crop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, phloem loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H+ symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic phloem loading and retrieval of sucrose leaking from the translocation path is not known. We therefor tested whether SWEETs are important for phloem loading in maize.\n\nHere we identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic phloem loading in Zea mays L. Notably, ZmSWEET13 paralogs (a, b, c) are among the highest expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants are severely stunted. Photosynthesis of mutants was impaired and leaves accumulated starch and soluble sugars. RNA-seq revealed profound transcriptional deregulation of genes associated with the photosynthetic apparatus and carbohydrate metabolism. GWAS analyses may indicate that variability in ZmSWEET13s is correlated with agronomical traits, specifically flowering time and leaf angle.\n\nThis work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in phloem loading in Zea mays L. Our study highlights these three ZmSWEET13 sucrose transporters as possible candidates for the engineering of crop yield.\n\nOne Sentence Summary: Three SWEET sucrose transporter paralogs are necessary for phloem loading in maize.

plant biology↗

bioRxiv2017

Matryoshka: Ratiometric biosensors from a nested 1 cassette of green- and orange-emitting fluorescent proteins

Sensitivity, dynamic and detection range as well as exclusion of expression and instrumental artifacts are critical for the quantitation of data obtained with fluorescent protein (FP)-based biosensors in vivo. Current biosensors designs are, in general, unable to simultaneously meet all these criteria. Here, we describe a generalizable platform to create dual-FP biosensors with large dynamic ranges by employing a single FP-cassette, named GO-(Green-Orange) Matryoshka. The cassette nests a stable reference FP (large Stokes shift LSSmOrange) within a reporter FP (circularly permuted green FP). GO-Matryoshka yields green and orange fluorescence upon blue excitation. As proof of concept, we converted existing, single-emission biosensors into a series of ratiometric calcium sensors (MatryoshCaMP6s) and ammonium transport activity sensors (AmTryoshka1;3). We additionally identified the internal acid-base equilibrium as a key determinant of the GCaMP dynamic range. Matryoshka technology promises flexibility in the design of a wide spectrum of ratiometric biosensors and expanded in vivo applications.

cell biology↗