Lotus japonicus WHY2 modulates root development via regulating auxin-repressor IAA14 expression

• Applicant: Dr. Thuy Linh Nguyen
• Subject Area: Plant Physiology ; Plant Cell and Developmental Biology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 563043005

The root system plays a crucial role in helping plants absorb nutrients, such as nitrate, from the soil. Under low nitrate conditions, plants enlarge their root surface area by growing more lateral roots, a process called ‘foraging’. Additionally, certain plants, like legumes, can obtain nitrogen via nodules - root symbiotic organs formed between host plants and nitrogen-fixing bacteria called rhizobia. Our preliminary work characterized a legume model (Lotus japonicus) mutant line containing non-functional version of the WHY2 gene. WHY2 belongs to a plant-specific transcription regulator family named WHIRLY involved in plant development and stress responses. Our preliminary investigations showed that legume plants lacking WHY2 had aberrant root systems and showed reduced overall plant performance. Phenotypic and transcriptomic data suggest that WHY2 may be important for coordinating nitrate-dependent root architectural adaptation. This appears to involve a role of WHY2 in mediating the activity of auxin, a plant hormon that is essential in regulating root development. Overall, the project aims to investigate (a) how WHY2 functions in root development and (b) in adapting root system architecture in the context of nitrogen acquisition strategies, and (c) how it is involved in auxin signaling. We will further analyze root development of Ljwhy mutant lines, focusing on lateral root initiation and the characterization of higher-order lateral roots. In addition, we will explore whether a role of WHY2 in root development is conserved across plant species by analyzing respective mutant lines of the nonsymbiotic model species thale cress (Arabidopsis thaliana). As legumes need to balance root and symbiosis development to optimize nitrogen uptake, investigating a putative role of WHY2 in this trade-off is another key project aim. Interestingly, both lateral root and nodule formation involve auxin signaling, which according to our preliminary work might be WHY2 regulated. This project aims to clarify how WHY2 integrates with the auxin-dependent regulatory network governing root and symbiosis development. One potential gene target of WHY2 is the auxin repressor called IAA14 (INDOLE-3-ACETIC ACID INDUCIBLE 14). Apart from testing this, we will also perform unbiased approaches to identify interaction partners and target genes of WHY2. Overall, the research project prosed here will broaden our mechanistic understanding of root architectural adaptation to the soil environment, such as nitrate availability and symbiotic potential. Furthermore, we will gain deeper insights in the role of WHY2 in auxin-driven root development.

• DFG Programme: WBP Position