The Evolution of Responses to Abiotic Factors in Leaves and Their Specialized Cell Types in the Tomato Family

摘要

The plant kingdom encompasses over 400,000 species which span the globe (Kew Royal Botanical Gardens, 2017) leaving the vast majority of plants genetically unexplored. The evolutionarily recent explosion of the angiosperms accounts for 369,000 of those species. This radical ability to speciate and adapt to diverse niches creates unique genetic footprints side-by-side with conserved genetic machinery. Advances in genetic, cellular, and molecular technologies allow modern scientists to pose hypotheses that were previously untestable (Levy & Myers, 2016) and open the way for comparative genetic explorations. The expansion in both breadth and depth of research gives rise to projects that allow broad taxonomic explorations of processes that have a more narrow focus. Within the tomato clade, I will explore morphology, physiology, and genetics in the context of abiotic stresses.;Chapter One investigates the morphological plasticity of the epidermis in Solanum lycopersicum LA4024 and Solanum habrochaites LA1777. Despite vastly different habitat niches, these two species both change epidermal patterning in response to water stress. Introgression Lines between these species allowed me to explore genetic regions controlling the regulation of epidermal patterning. The underlying regulatory mechanisms of epidermal patterning in tomato are controlled by multiple genetic loci, are distributed widely in the genome, and are independently controlled for abaxial and adaxial leaf surfaces.;The second chapter dives into submergence stress whereby the levels of genetic regulation are dissected using Isolated Nuclei TAgged in specific Cell Types (INTACT) and Translating Ribosome Affinity Purification (TRAP) in seedlings of Solanum lycopersicum var M82 and Solanum pennellii LA0716. These new molecular techniques applied to highly related species, whose niches are so far diverged, offers insights into responses elicited at different regulatory levels in different tissues. Surprisingly, the two Solanum species showed inconsistencies in their responses to submergence stress in both expression pattern and regulatory level. Further investigation within species and across regulation levels most notably revealed that the desert-adapted, wild tomato species S. pennellii experiences and responds to hypoxic conditions on commonly used media even before the onset of submergence. These regulatory clues may also help clarify the specificity of stress response pathways with continued experiments.;The third chapter examines physiological and morphological responses in S. lycopersicum var M82 after 11 days of Waterlogged and Insufficient Water conditions. A broad set of measurements, shown previously to correlate with stress, were used to define a narrower subset of these metrics that correlates with precise, repeatable abiotic stresses of sufficient length to allow us to explore sublethal abiotic stresses in growth chamber conditions. Root and shoot phenotypes were thus more easily monitored and provided new insights. Increased hypocotyl-derived roots and root cell populations marked Waterlogged individuals while a decrease in photosynthetic rates and leaflet relative water content marked insufficiently watered individuals. Though sequencing data for both INTACT RNAseq and Assay for Transposase-Accessible Chromatin using sequencing (ATACseq) was too shallow to definitively dissect genetic responses, an increase in biological replicates and tissue sample quantities should resolve this in future endeavors.