Long Lab: Biochemistry of plant-­‐‑microbe signals Background: • Rhizobium bacteria establish N2-­‐‑fixing symbioses with plant hosts in the legume family. • A complex, specific developmental process occurs to form a plant root nodule infected by bacteria. Both partners undergo marked differentiation during nodule development. Primary Questions: • How do the eukaryote and prokaryote recognize each other? In early nodulation, they exchange plant flavonoids1 and bacterially-­‐‑produced Nod factors (modified oligosaccharides). Other stages of symbiosis such as invasion2 are not understood. We use genetics to find stage-­‐‑specific markers for developmental events and to ask what plant cues regulate expression of bacterial symbiosis genes • How is the bacterial cell envelope changed during infection, and what environmental conditions in the plant trigger these responses? Systems of study: • Sinorhizobium meliloti, a N2-­‐‑fixing species in the α-proteobacteria clade • Medicago truncatula, a diploid model legume related to alfalfa Approaches: •
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bacteria and plants -­‐‑ forward genetic screens, reverse genetics use of plant and bacterial mutants to analyze signal exchange mechanisms genomic and global transcription analyses fluorescence microscopic study of cell dynamics in vitro transcription, protein purification, modeling, mutational analysis luteolin, a plant flavonoid, interacts with bacterial NodD transcription factor 1
Free-­‐‑living bacteria Bacteria (blue stain) invade a plant root 2