Biology subjects

Zoellner, N.

Publications and source records attributed to Zoellner, N..

4 recordsLinked to original sources

bioRxiv2026

Cell identities along the proximal-distal and micropylar-chalazal axes in the Arabidopsis heart-stage seed

* Seeds are complex reproductive organs consisting of diverse maternal and filial tissues. During development, the embryo and specialized tissues for nutrient storage required for seed germination and early seedling establishment emerge. * To explore the cellular diversity and differentiation of seeds, we performed single cell RNA-sequencing on heart stage Arabidopsis seeds and identified 20,097 cells that were grouped into [≥]21 distinct cell clusters. 20 of the 21 clusters were spatially assigned by combining bioinformatic analysis, imaging reporter fusion marker lines, and spatial transcriptomics. * Our analysis revealed a high degree of differentiation of epidermal cell and inner cell layers along the rotational and axial seed axes, highlighting the importance of cell position and ontogenesis. We identified unexpected spatial domains, including a cluster marked by abscission zone-specific transcripts, and a nucellar cluster shaped by developmentally programmed cell death. Surprisingly, embryo and endosperm showed similarities in transcript profiles despite distinct and complementary functions. * In summary, our findings establish seeds as a transcriptionally complex organ with high cell type heterogeneity and provide a basis for investigating the differentiation of diverse cell layers and spatial transcript profiles.

cell biology↗

bioRxiv2025

Evidence for rapid hydrolysis of shoot-derived sucrose using an ultrasensitive ratiometric Matryoshka-type MGlucoMeter sensor

To enable sensitive in vivo monitoring of the glucose transport and metabolism, we developed a series of ultrasensitive and ratiometric genetically encoded nanosensors by inserting a Matryoshka dual fluorophore cassette consisting of cpsfGFP and LSSmApple into the glucose binding protein ttGBP from Thermus thermophilus. The initial MGlucoMeter1.0 was subjected to an alanine scan of the hinge region producing more sensitive MGlucoMeter2.6 with a glucose-induced {Delta}F/F0 change of 3.0, an affinity for glucose of 15 {micro}M, and an approximate detection range of 1.1-216 {micro}M. To generate variants suitable for in vivo measurements, a series of affinity mutants was generated by mutating two histidines predicted to be involved in substrate binding. MGlucoMeter2.6-353n, MGlucoMeter2.6-15{micro}, MGlucoMeter2.6-700{micro}, MGlucoMeter2.6-1m, and MGlucoMeter2.6-7m cover a detection range between [~]40 nM - 55 mM. When expressed from a ubiquitous promoter in the cytosol of the Arabidopsis gene silencing mutant rdr6, MGlucoMeter2.6-1m reports time- and concentration-dependent accumulation of glucose in seedling roots. The sensor also detects rapid hydrolysis of shoot-derived sucrose in the root tip.

plant biology↗

bioRxiv2025

A critical role of sux cistron-mediated sucrose uptake for virulence of the rice blight pathogen Xanthomonas oryzae pv. oryzae

The virulence of Xanthomonas oryzae pv. oryzae, the causal agent of bacterial blight (BB) of rice, critically depends on the activation of SWEET sucrose uniporters of the host. To date, the role of SWEET-released sucrose for virulence remains unclear. We here identified the sux locus of Xoo, consisting of a LacI-type repressor (SuxR), an outer membrane TonB-like porin (SuxA), an inner membrane MFS H+-symporter (SuxC), and a cytosolic sucrose hydrolase (SuxB). Structural and functional analyses demonstrate that SuxB has exclusive sucrose hydrolase activity. Mutant analyses show that the transporter SuxC and the sucrose hydrolase are necessary for growth of bacteria on sucrose, while SuxA is not essential, likely due to the ability of other porins to transport sucrose across the outer membrane. Consistent with a role of SuxR as a sucrose repressor, transcriptome studies show sucrose-dependent regulation of the suxA/suxB genes. Besides a role of sucrose for reproduction, we found that sucrose promotes motility, EPS production, biofilm formation, and virulence. Notably, the SuxC sucrose H+-symporter and the sucrose hydrolase SuxB were required for full virulence of Xoo on indica and japonica rice varieties. Our findings indicate that pathogen-induced sucrose efflux via SWEETs provides sucrose to Xoo, that Xoo uses the sux gene cluster to acquire and utilize sucrose, and that sucrose promotes bacterial fitness and xylem colonization. Significance StatementUnderstanding disease mechanisms is critical for developing strategies to protect plants against infections. Bacterial blight, a major threat to global rice production, is caused by Xanthomonas oryzae pv. oryzae strains that hijack rice SWEET sucrose uniporters. Xanthomonas oryzae pv. oryzae deploys a set of molecular "keys", TAL effectors, to trigger host sucrose release. Sugars could serve as nutrients for the bacteria or prime host defense. Here, we provide evidence that the pathogens ability to attack and grow depends on sucrose uptake. We explore how crucial virulence functions, such as motility, EPS production, and biofilm formation, depend on the activity of the sucrose utilization system, supporting a key role of sucrose for the nutrition of the bacteria in the xylem.

microbiology↗

bioRxiv2020

Phloem loading via the abaxial bundle sheath cells in maize leaves

Leaves are asymmetric, with differential functionalization of abaxial and adaxial tissues. The bundle sheath (BS) surrounding the vasculature of the C3 crop barley is dorsoventrally differentiated into three domains: adaxial structural, lateral S-type, and abaxial L-type. S-type cells seem to transfer assimilates towards the phloem. Here we used single-cell RNA sequencing to investigate BS differentiation in C4 maize. Abaxial BS (abBS) cells of rank-2 intermediate veins specifically expressed three SWEET sucrose uniporters (SWEET13a, b, and c) and UmamiT amino acid efflux transporters. SWEET13a, b, c were also identified in the phloem parenchyma (PP). Thus maize acquired a unique mechanism for phloem loading in which abBS cells provide the main pathway for apoplasmic sucrose transfer towards the phloem. This pathway predominates in veins responsible for phloem loading (rank-2 intermediate), while rank-1 intermediate and major veins export sucrose from the phloem parenchyma (PP) adjacent to the sieve element companion cell (SE/CC) complex, as in Arabidopsis. We surmise that abBS identity is subject to dorsoventral patterning and has components of PP identity. These observations provide first insights into the unique transport-specific properties of abBS cells and support for a modification to the canonical phloem loading pathway of maize, which may be generalizable to other C4 monocots.

plant biology↗