Non-linear relationships between gene expression and physiological traits. For each trait, all transcripts with significant non-linear relationships are shown (MIC P < 0.05 after Bonferroni correction, |r| < 0.8). Transcripts showing similar patterns were grouped by hierarchical clustering of dissimilarity matrices. Each line represents a series of paired expression data and physiological measurements smoothed using local polynomial regression (span = 0.8). Arrows indicate the direction of change during drought, from the average in control plants (base of arrow) to the average in stressed plants (arrowheads). (a, b) n = 162 transcripts showing non-linear relationships with predawn leaf water potential. (c, d) = 51 transcripts showing non-linear relationships with photochemical quenching. Panels a and d depict genes expressed at higher levels in the control than the drought treatment, and vice versa for panels b and c.