Codominant grasses differ in gene expression under experimental climate extremes in native tallgrass prairie

Abstract

Extremes in climate, such as heat waves and drought, are expected to become more frequent and intense with forecasted climate change. Plant species will almost certainly differ in their responses to these stressors. We experimentally imposed a heat wave and drought in the tallgrass prairie ecosystem near Manhattan, Kansas, USA to assess transcriptional responses of two ecologically important C₄ grass species, Andropogon gerardii and Sorghastrum nutans. Based on previous research, we expected that S. nutans would regulate more genes, particularly those related to stress response, under high heat and drought. Across all treatments, S. nutans showed greater expression of negative regulatory and catabolism genes while A. gerardii upregulated cellular and protein metabolism. As predicted, S. nutans showed greater sensitivity to water stress, particularly with downregulation of non-coding RNAs and upregulation of water stress and catabolism genes. A. gerardii was less sensitive to drought, although A. gerardii tended to respond with upregulation in response to drought versus S. nutans which downregulated more genes under drier conditions. Surprisingly, A. gerardii only showed minimal gene expression response to increased temperature, while S. nutans showed no response. Gene functional annotation suggested that these two species may respond to stress via different mechanisms. Specifically, A. gerardii tends to maintain molecular function while S. nutans prioritizes avoidance. Sorghastrum nutans may strategize abscisic acid response and catabolism to respond rapidly to stress. These results have important implications for success of these two important grass species under a more variable and extreme climate forecast for the future.

Keywords: Andropogon gerardii; C4 grass; Dominant species; Drought; Heat wave; Microarray; Sorghastrum nutans.

Figure 1. Differentially expressed genes in A. gerardii and S. nutans.

Differentially expressed genes have a log₂ fold change greater than one, shown as colored points where p < 0.05. Positive values indicate greater expression in A. gerardii while negative values indicate greater expression in S. nutans. Filled circles represent genes belonging to selected Gene Ontology groups. Open circles: red, differentially expressed, gray, not significantly different.

Figure 2. Gene modules explaining species differences under different water availability.

Gene modules detected explaining species differences in watered (A) and drought (B, C) conditions. Sample names are presented on the x-axis, where each label applies to two columns of the same description (e.g., Ag. W.H applies to the first two columns, but both are replicates of A. gerardii in Watered plot with Heated treatment). Ag, A. gerardii, Sn, S. nutans, W, watered, D, drought, H, heated, A, ambient temperature. No annotation found, N.A.

Figure 3. Differentially expressed genes in response to water availability.

Differentially expressed genes in (A) A. gerardii and (B) S. nutans only compared between watered and drought plots (12 and 13). Significantly different genes with log₂ fold change greater than one are represented by colored points where p < 0.05. Positive values indicate greater expression in the watered plot while negative values indicate greater expression in the drought plot. Filled circles represent genes belonging to selected Gene Ontology groups. Open circles: red, differentially expressed, gray, not significantly different.