Linking gene regulation, physiology, and plant biomass allocation in Andropogon gerardii in response to drought

Plant responses to drought are often initiated at the molecular level and cascade upwards to affect physiology and growth. How plants respond to and recover from drought have consequences for their growth and survival in drier climates predicted with climate change. We studied four ecologically relevant genotypes of a common C4 grass, Andropogon gerardii. These genotypes had differential responses to a decade of more variable precipitation patterns in a field experiment in native tallgrass prairie. Here, we conducted a greenhouse experiment examining how these genotypes responded to repeated 10-day drought-recovery cycles when experiencing either a severe or moderate drought. We did this twice over the course of the experiment, early, after 5 weeks, and late, after 9 weeks of drought. We studied nine genes involved in water stress signaling and drought response in leaf tissue using real-time reverse-transcriptase polymerase chain reaction (qRT-PCR). We also measured photosynthesis, stomatal conductance, and biomass accumulation and allocation. In early drought, we found consistent differences among genotypes in gene expression, leaf-level physiology, and biomass accumulation and allocation. We found genes involved in ABA, proline synthesis, and mitigating oxidative stress were differentially expressed between genotypes, while genes that coded for aquaporins and chaperones were not. In late drought, we found fewer overall differences, and little regulation of drought responsive genes. Ultimately, we found genotypes either had greater phenotypic plasticity, suggesting an ability to avoid drought and maximize water resources when they were present, or genotypes were better at tolerating drought.