Biology subjects

Zierer, W.

Publications and source records attributed to Zierer, W..

8 recordsLinked to original sources

bioRxiv2026

Reducing transitory starch in cassava impairs photosynthesis and carbon export to storage roots

Optimizing source-sink relations is a central strategy for improving crop yield. In potato, reducing transitory leaf starch synthesis can redirect carbon to storage organs without impairing growth. To test whether this strategy is transferable to cassava, we suppressed the major small subunit of ADP-GLUCOSE PYROPHOSPHORYLASE, MeAPS1a. Transgenic plants were nearly devoid of transitory leaf starch and showed impaired photosynthetic carbon fixation. Under greenhouse conditions, shoots acclimated to the reduced carbon supply and exhibited only moderate biomass losses, and the data indicated reduced carbon supply to developing storage roots. This was reflected by lower leaf sucrose levels, reduced storage root biomass and starch accumulation, and downregulation of carbohydrate-responsive genes, including the major AGPase large subunit MeAPL3. Under field conditions, the absence of transitory starch was even more detrimental, causing severe growth inhibition and drastic reductions in both shoot and root biomass. We also found that MeAPS1a-derived small interfering RNAs moved systemically from leaves to roots, with lower root siRNA abundance in older, larger plants than in younger, smaller plants. Together, our results demonstrate that transitory starch is indispensable for sustaining carbon flux to cassava storage roots, highlighting species-specific constraints on engineering source-sink relations.

plant biology↗

bioRxiv2026

Repeatability and Heritability of UAV-Derived Canopy Traits in a Cassava Breeding Population Using Time-Series Data from Two Consecutive Growing Seasons

Cassava is a major staple crop in tropical regions, particularly in Sub-Saharan Africa, yet its productivity remains constrained by genetic and agronomic limitations. A major bottleneck in cassava breeding is the difficulty of accurately phenotyping agronomic traits under field conditions using conventional, labor-intensive methods. Here, we evaluated the potential of uncrewed aerial vehicle (UAV)-based phenotyping to quantify canopy growth traits and assess their genetic relevance under realistic field conditions. For this, multi-temporal UAV imagery was collected over two growing seasons (2018-2019 and 2019-2020) in a panel of 46 cassava genotypes planted in fields of the International Institute for Tropical Agriculture (IITA), Nigeria. Canopy height, canopy volume, and their relative growth rates (RGRh and RGRv) were extracted at the plot-level, and their seasonal dynamics and canopy-yield relationships were further assessed across developmental stages and environmental conditions. Repeatability (R) and broad-sense heritability (H2) were estimated using a linear mixed model (LMM) that partitioned genetic, genotype-by-year, and residual variance components, enabling the evaluation of both measurement reliability and genetic signal. Overall, UAV-derived growth dynamics were found to exhibit comparable patterns across genotypes, reflecting shared seasonal growth trajectories, while canopy-yield relationships varied with developmental stage and environmental conditions. In terms of genetic metrics, R was high for all UAV-derived traits (R = 0.68-0.69), indicating reliable genotype-level assessment across replicates and seasons. In contrast, H2 differed substantially among traits. Canopy volume (H2 = 0.64) and canopy height (H2 = 0.58) exhibited moderate-to-high heritability, reflecting strong genotype effects and comparatively moderate genotype-by-year interactions. However, their relative growth rates showed near-zero H2 values, driven primarily by genotype-by-year interaction, indicating a dominant environmental influence. These results demonstrate that UAV-derived canopy height and volume provide a consistent basis for genetic differentiation of cassava genotypes across environments, supporting their use in selection, whereas growth-rate traits are better suited for characterizing growth plasticity and genotype-by-environment interactions.

plant biology↗

bioRxiv2025

A non-rectifying potassium channel increases cassava drought tolerance and storage root yield

Cassava (Manihot esculenta) is an important crop for food security in the tropics, particularly for smallholder farmers in sub-Saharan Africa, where yields are often severely limited by pathogen pressure, nutrient deficiency, and water scarcity. We expressed a non-rectifying Arabidopsis thaliana potassium (K+) channel gene version, AKT2var, in the vascular tissue of cassava plants. The transgenic cassava plants had higher electron transport and CO2 assimilation rates, a higher bulk flow velocity, and increased source-sink carbohydrate transport, as demonstrated by comparative 11C-positron emission tomography and tissue-specific metabolite profiling. Cassava storage root yield was significantly increased in greenhouse experiments and in a multi-year field trial conducted under subtropical conditions. AKT2var plants were also more tolerant to drought stress and had higher storage root yield. Targeted alteration of K+ transport is therefore a promising strategy to improve cassava productivity without additional fertilizer input and in climate-adverse growing conditions.

plant biology↗

bioRxiv2025

High-resolution spatial transcriptomics of stem and storage root vascular cambia highlights key regulatory processes for xylem parenchyma differentiation in cassava

Due to their high carbohydrate content, the storage roots of cassava are an important food source for hundreds of millions of people worldwide. In contrast to the woody stems of the plant, the xylem of the storage roots produces mainly starch-rich storage parenchyma cells and only few tracheary elements and almost no fibers. Despite these obvious differences, both stems and storage roots are formed by a vascular cambium. To find more insights into the differences in the regulation of cell division and differentiation in stems and storage roots, a cryo-sectioning approach was utilized, to generate high-resolution transcriptome profiles spanning the entire vascular cambium of both tissues. We observed that storage parenchyma formation is connected to the repression of secondary cell wall formation through a decrease in expression levels of key players in the NAC/MYB regulatory network, as well as decreases in the downstream pathways for lignin and hemicellulose biosynthesis. Additionally, the expression of MeWOX14, a transcription factor associated with GA signaling and xylem fiber differentiation, is strongly reduced in storage roots compared to stem xylem. By contrast, the expression of MeKNOX1, a well-known meristem regulator, as well as most cassava LSH genes and several ABA-related transcription factors were associated with parenchyma cells. Our data suggest that the repression of secondary cell wall formation and GA signaling, together with an active auxin and ABA signaling, as well as extended MeKNOX1 activity could control storage parenchyma formation in cassava storage roots. Significance statementTissue-specific expression data is still scarce for cassava and the regulatory mechanisms controlling the formation and differentation of secondary vasculature cells are largely unknown in this species. By performing a cryosectioning approach on cassava stems and storage roots, we generated highly-resolved, tissue-specific transcriptomic data, identified key factors for parenchyma cell formation in storage roots and propose a working model for further research.

plant biology↗

bioRxiv2024

Symplasmic phloem loading and sub-cellular transport in storage roots are key factors for carbon allocation in cassava

Cassava is a deciduous woody perennial shrub that stores large amounts of carbon and water in its storage roots. Previous studies have shown that assimilate unloading into storage roots happens symplasmically once secondary anatomy is established. However, mechanisms controlling phloem loading and overall carbon partitioning to different cassava tissues remain unclear. Here we used a combination of histological, transcriptional, and biochemical analyses on different cassava tissues and timepoints to better understand source-sink carbon allocation. We find that cassava likely utilizes a predominantly passive symplasmic phloem loading strategy, indicated by the lack of expression of genes coding for key players of sucrose transport, the existence of branched plasmodesmata in the companion cell/bundle sheath interface of minor leaf veins, and very high leaf sucrose concentrations. Furthermore, we show that tissue-specific changes in anatomy and NSC contents are associated with tissue-specific modification in gene expression for sucrose cleavage/synthesis, as well as subcellular compartmentalization of sugars. Overall, our data suggest that carbon allocation during storage root filling is mostly facilitated symplasmically, and is likely mostly regulated by local tissue demand and subcellular compartmentalization.

plant biology↗

bioRxiv2023

Carbon usage in yellow-fleshed Manihot esculenta storage roots shifts from starch biosynthesis to cell wall and raffinose biosynthesis via the myo-inositol pathway

Cassava is a crucial staple crop for smallholder farmers in tropical Asia and Sub-Saharan Africa. Although high yield remains the top priority for farmers, the significance of nutritional values has increased in cassava breeding programs. A notable negative correlation between provitamin A and starch accumulation poses a significant challenge for breeding efforts. The negative correlation between starch and carotenoid levels in conventional and genetically modified cassava plants implies the absence of a direct genomic connection between the two traits. The competition among various carbon pathways seems to account for this relationship. In this study, we conducted a thorough analysis of 49 African cassava genotypes with varying levels of starch and provitamin A. Our goal was to identify factors contributing to differential starch accumulation. With the carotenoid levels of the varieties considered as a confounding effect on starch production, we found that yellow and white-fleshed storage roots did not differ significantly in most measured components of starch or de novo fatty acid biosynthesis. However, genes and metabolites associated with myo-inositol synthesis and cell wall component production were substantially enriched in high provitamin A genotypes. These results indicate that yellow-fleshed cultivars, in comparison to their white-fleshed counterparts, direct more carbon towards the synthesis of raffinose and cell wall components, a finding that is supported by a significant rise in the starch-free residue to total dry yield ratio in yellow storage roots versus white storage roots. Our findings enhance comprehension of the biosynthesis of starch and carotenoids in the storage roots of cassava.

plant biology↗

bioRxiv2021

Cold-triggered induction of ROS- and raffinose metabolism in freezing-sensitive taproot tissue of sugar beet

Sugar beet (Beta vulgaris subsp. vulgaris) is the exclusive source of sugar in the form of sucrose in temperate climate zones. There, sugar beet is grown as an annual crop from spring to autumn because of the damaging effect of freezing temperatures to taproot tissue. Natural and breeded varieties display variance in the degree of tolerance to freezing temperatures and genotypes with elevated tolerance to freezing have been isolated. Here we compare initial responses to frost between genotypes with either low and high winter survival rates. The selected genotypes differed in the severity of frost injury. We combined transcriptomic and metabolite analyses of leaf- and taproot tissues from such genotypes to elucidate mechanisms of the early freezing response and to dissect genotype- and tissue-dependent responses. Freezing temperatures induced drastic downregulation of photosynthesis-related genes in leaves but upregulation of genes related to minor carbohydrate metabolism, particularly of genes involved in raffinose metabolism in both, leaf and taproot tissue. In agreement with this, it has been revealed that raffinose and the corresponding intermediates, inositol and galactinol, increased markedly in these tissues. We found that genotypes with improved tolerance to freezing, showed higher accumulation of raffinose in a defined interior region within the upper part of the taproot, the pith, representing the tissue most susceptible to freeze damages. This accumulation was accompanied by specific upregulation of raffinose synthesizing enzymes in taproots, suggesting a protective role for raffinose and its precursors for freezing damage in sugar beet.

plant biology↗

bioRxiv2020

Vernalization alters sugar beet (Beta vulgaris) sink and source identities and reverses phloem translocation from taproots to shoots

During vegetative growth, biennial sugar beets maintain a steep gradient between the shoot (source) and the sucrose-storing taproot (sink). To shift from vegetative to generative growth, they require a chilling phase, called vernalization. Here, we studied sugar beet sink-source dynamics upon cold temperature-induced vernalization and revealed a pre-flowering taproot sink to source reversal. This transition is induced by transcriptomic and functional reprogramming of sugar beet tissue, resulting in a reversal of flux direction in long distance transport system, the phloem. As a key process for this transition, vacuolar sucrose importers and exporters, BvTST2;1 and BvSUT4, are oppositely regulated, leading to re-mobilization of sugars from taproot storage vacuoles. Concomitant changes in the expression of floral regulator genes suggest that the now deciphered processes are a prerequisite for bolting. Our data may thus serve dissecting metabolic and developmental triggers for bolting, which are potential targets for genome editing or breeding approaches.

plant biology↗