Date of Award

5-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean Engineering and Marine Sciences

First Advisor

Andrew G. Palmer

Second Advisor

Christopher A. Bashur

Third Advisor

David Carroll

Fourth Advisor

Eric Guisbert

Abstract

Many organisms have evolved to identify and respond to differences in genetic relatedness between conspecifics, allowing them to select between competitive and facilitative strategies to improve fitness. Due to their sessile nature, plants frequently draw from the same pool of nutrients, and the ability to limit competition between closely related conspecifics would be advantageous. Over the last 3 decades, significant evidence has accumulated in multiple species that such ‘kin recognition’ (KR) is indeed commonplace in plants. I propose that if KR has evolved, at least in part, as a plant-plant interaction to regulate nutrient uptake, then nutrients should modulate the KR response. There are few model systems for understanding KR interactions. The discovery that Arabidopsis thaliana is capable of KR provides an important resource for understanding the molecular and biochemical underpinnings of this process, as well as the phenotypic and physiological processes. In this dissertation, I have leveraged the advantages of Arabidopsis to determine if and how nutrient availability impacts KR in this model angiosperm from germination to flowering. I have utilized phenotypic as well as metabolomic assays to interrogate this system. Preliminary studies with Arabidopsis confirmed that these plants identify ‘kin’ as members of the same accession (geographical variations), and alter their root system architecture (RSA) in response. Phenotypic assays confirmed that nutrient availability, specifically nitrogen, was the major modulator of KR responses in Arabidopsis seedlings. Our experiments further confirmed that signals necessary for KR were present in the root exudates of these seedlings and that sensitivity to these signals was modulated by nutrient availability. This observation has since been documented in other plant systems. However, whether the KR response changes over time remains unclear for most systems. By coupling phenotypic assays to mass spectrometry-based studies of primary metabolite distribution, we provided preliminary insight into the biochemical underpinnings of the changes observed during these plant-plant responses. I identified root and shoot traits that are affected by nutrient-mediated accession recognition. Most notably that late-stage changes in sucrose metabolism in members of the same accession drove early flowering (Chapter 3). Finally, I investigated how nutrient availability impacted the composition of the root exudates, the primary source of KR signals throughout the plant’s life-cycle (Chapter 4). This work established significant changes in exudate composition as both a function of neighbor identity as well nutrient availability. Perhaps paradoxically, under reduced nutrient availability I see an increase in exudate production and diversity between interacting plants of different accessions. Such increased chemical complexity within the rhizosphere could change microbiome recruitment, modify growth of neighboring plants, and potentially alter nutrient uptake. Such chemical diversity also allowed us to distinguish between two distinct models for how identity information may be conveyed. Our work underscores the need to evaluate accession-recognition under the context of nutrient availability and consider responses throughout the plant’s life, not simply at the earliest stages of interaction. This system provides the first plant system for an evaluation of nutrient utilization in the context of KR, a crucial piece of information for understanding how KR functions. Moreover, our findings impact our broader understanding of the KR phenomenon, as well as some elucidation of the strategies used by A. thaliana during KR.

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