Biology subjects

Mai, H.-J.

Publications and source records attributed to Mai, H.-J..

5 recordsLinked to original sources

bioRxiv2026

FE DEFICIENCY-INDUCED KELCH REPEAT PROTEIN 1 (FDK1) links coumarin metabolism and iron homeostasis during alkaline iron deficiency in Arabidopsis

Although iron (Fe) is abundant in soils, its low solubility, particularly under alkaline conditions, often limits plant Fe acquisition. Under these conditions, coumarin-mediated Fe mobilization becomes increasingly important. Arabidopsis thaliana FE DEFICIENCY-INDUCED KELCH REPEAT PROTEIN 1 (FDK1, AT3G07720) is strongly induced by Fe deficiency and regulated by the central transcription factor FIT, but its function is unknown. We investigated FDK1 using genetic, physiological, metabolite, and transcriptomic analyses. Loss of FDK1 altered root growth, whereas this phenotype was restored in the FDK1-Ox overexpression line. Under alkaline Fe deficiency, growth medium from FDK1-Ox contained strongly increased levels of the Fe-mobilizing coumarins fraxetin and esculetin compared with wild type, whereas their induction was attenuated in fdk1-1. RNA-seq analysis linked FDK1 abundance to coumarin biosynthesis and iron-homeostasis gene expression. FIT and many FIT-associated genes were highly expressed in FDK1-Ox, whereas several upstream iron-homeostasis regulators, including bHLH Ib factors, were highest in fdk1-1. These findings identify FDK1 as a component of the alkaline Fe-deficiency response that promotes iron-mobilizing coumarin accumulation and is associated with coordinated regulation of iron-homeostasis genes.

plant biology↗

bioRxiv2025

Balancing nutrient remobilization and photosynthesis: the dual role of lupin cotyledons after germination

Efficient nutrient mobilization from seed storage tissues is essential for seedling establishment, particularly in legumes such as Lupinus albus (white lupin), which thrive in nutrient-poor soils. This study investigates the role of cotyledons in nitrogen (N) and mineral remobilization after germination during their transition from storage organs to photosynthetically active tissues including the metabolic challenges posed by coexistence of these two functions in epigeal germination. We cultivated white lupin seedlings under nitrogen-deficient conditions, analyzing cotyledon composition and function over 28 days. Our results indicate that 60 % of cotyledon-stored proteins are degraded within the first eight days, with free amino acids transiently accumulating before being redistributed to support growth. The progressive depletion of cotyledon reserves was accompanied by structural and metabolic changes, including an increase in photosynthetic proteins. However, cotyledon photosynthetic capacity remained lower than that of true leaves, suggesting a transient role in energy metabolism. The loss of cotyledons before day 12 significantly impaired seedling development, emphasizing their critical contribution to nitrogen, phosphate, and micronutrient supply during early growth. Comparative proteomic analysis revealed dynamic shifts in nutrient transport, amino acid metabolism, and stress response pathways following cotyledon removal. These findings underscore the significance of cotyledon nutrient remobilization in legume adaptation to low-fertility soils and highlight potential targets for breeding strategies aimed at improving nutrient use efficiency. By optimizing cotyledon nutrient composition and function, future breeding efforts could enhance seedling vigor, reduce fertilizer dependency, and improve the nutritional value of lupin-based foods. Significance statementThis study uncovers how white lupin cotyledons balance nutrient storage and photosynthesis during early seedling development, ensuring sustained nitrogen and mineral supply under nutrient-deficient conditions. By detailing the proteome reorganization and consequences of premature cotyledon loss, it identifies key mechanisms supporting seedling resilience and adaptation to low-fertility soils.

plant biology↗

bioRxiv2024

Iron homeostasis in the annual and perennial stem zones of Arabis alpina

Plants serve as reservoirs for vital micronutrients, including iron, which they store in bioavailable forms to support growth in subsequent seasons. The perennial life style is preponderant in nature. Annual species allocate iron towards their seeds. However, our understanding of iron homeostasis in perennial plants remains limited. Arabis alpina is a perennial model organism. Its perenniating branches undergo secondary growth where they store carbon-rich macromolecules. In this study, we investigated iron homeostasis in the perennial and annual stem zones (PZ, AZ) of A. alpina. We found that both, the wild-type Pajares (Paj) and perpetual flowering 1 mutant accumulated iron at various developmental stages in the PZ as well as in the AZ. Notably, iron levels in the PZ were found to be approximately two-fold higher than those in the AZ, underscoring the PZs enhanced capacity for iron storage, irrespective of flowering status. Iron was predominantly located within plastid-bound ferritin, providing insight into its storage mechanism. Furthermore, gene expression analyses supported the significance of ferritin and demonstrated an enrichment of transcripts related to iron homeostasis within the stems. Distinct patterns of expression among iron homeostasis genes were observed in relation to iron contents in the PZ and AZ, indicating tissue-specific regulatory mechanisms governing iron accumulation. These findings collectively emphasize the critical function of secondary growth and the PZ as an important site for iron storage in perennial plants, suggesting thatfuture research should further explore the nuances of iron homeostasis signaling in perennial plants. Highlight- Iron accumulates in the perennial stem zone, and ferritin is a storage form for iron there. - Transcripts of iron homeostasis genes are enriched among genes expressed in the annual and perennial stem zones, yet iron accumulation correlates with different gene expression patterns.

plant biology↗

bioRxiv2020

Cytokinin-promoted secondary growth and nutrient storage in the perennial stem zone of Arabis alpina

Perennial plants maintain their life span through several growth seasons. Arabis alpina serves as model Brassicaceae species to study perennial traits. A. alpina lateral stems have a proximal vegetative zone with a dormant bud zone, and a distal senescing seed-producing inflorescence zone. We addressed the questions of how this zonation is distinguished at the anatomical level, whether it is related to nutrient storage, and which signals affect the zonation. We found that the vegetative zone exhibits secondary growth, which we termed the perennial growth zone (PZ). High-molecular weight carbon compounds accumulate there in cambium and cambium derivatives. Neither vernalization nor flowering were requirements for secondary growth and sequestration of storage compounds. The inflorescence zone with only primary growth, termed annual growth zone (AZ), or roots exhibited different storage characteristics. Following cytokinin application, cambium activity was enhanced and secondary phloem parenchyma was formed in the PZ and also in the AZ. In transcriptome analysis cytokinin-related genes represented enriched gene ontology terms and were expressed at higher level in PZ than AZ. Thus, A. alpina uses primarily the vegetative PZ for nutrient storage, coupled to cytokinin-promoted secondary growth. This finding lays a foundation for future studies addressing signals for perennial growth. HighlightArabis alpina stems have a perennial zone with secondary growth, where cambium and derivatives store high-molecular weight compounds independent of vernalization. Cytokinins are signals for the perennial secondary growth zone.

plant biology↗

bioRxiv2020

Transcriptomic expression patterns of two contrasting lowland rice varieties reveal high iron stress tolerance

Iron (Fe) toxicity is a major challenge for plant cultivation in acidic water-logged soil environments, where lowland rice is a major staple food crop. Only few studies addressed the molecular characterization of excess Fe tolerance in rice, and these highlight different mechanisms for Fe tolerance in the studied varieties. Here, we screened 16 lowland rice varieties for excess Fe stress growth responses to identify contrasting lines, Fe-tolerant Lachit and -susceptible Hacha. Hacha and Lachit differed in their physiological and morphological responses to excess Fe, including leaf growth, leaf rolling, reactive oxygen species generation, Fe and metal contents. These responses were mirrored by differential gene expression patterns, obtained through RNA-sequencing, and corresponding GO term enrichment in tolerant versus susceptible lines. From the comparative transcriptomic profiles between Lachit and Hacha in response to excess Fe stress, individual genes of the category metal homeostasis, mainly root-expressed, may contribute to the tolerance of Lachit. 22 out of these 35 metal homeostasis genes are present in selection sweep genomic regions, in breeding signatures and/or differentiated during rice domestication. These findings will serve to design targeted Fe tolerance breeding of rice crops. Summary statementLowland rice varieties Hacha and Lachit were selected for contrasting abilities to cope with iron excess stress. Morphological and physiological phenotypes were mirrored by molecular transcriptome changes, indicating altered metal homeostasis in the root as an adaptive tolerance mechanism in Lachit.

plant biology↗