Figure 4: Stress-responsive gene expression levels as predictors for heterosis and effects of cold stress and SA on growth rate.

(a,b) Relative expression levels (R.E.L.) of ACD6 (a) and COR78 (b) in 10 ecotypes at ZT0, ZT9 and ZT18. Values are averages from three biological replicates (±s.d.). C24 (dashed-box) has higher ACD6 and lower COR78 expression levels than Col, Ler and Ws (grey boxes). (c–e) Biomass increase relative to MPV (y axis) in various hybrids was plotted against absolute values of the log₂-fold expression level changes (x axis) in different stress genes at three time points (ZT0, 9 and 18). Scatter plots for ACD6 at ZT18 (c), COR78 at ZT9 (d) and COR47 at ZT9 (e). Regression lines (red) were statistically significant for ACD6 at ZT18 (c), COR78 at ZT9 (d) and COR47 at ZT9 (e). Data used to perform regression analyses were shown in Supplementary Table 3, and detailed results of the analysis were included in Supplementary Data 3. (f,g) Rosette diameters of seedlings (n=15 plants averaged per replicate) that were grown at 22 ^oC (f) or 4 ^oC (g) for 17 days and transferred to grow in soil for another 8 days at 22 °C. (h,i) Rosette diameters of seedlings (n=15 plants averaged per replicate) that were mock-treated (h) or treated with SA twice (indicated by arrows; SA) (i) and were transferred to soil for another 8 days. Values were averaged from three biological replicates (mean±s.d.). Single and double asterisks indicate statistically significant levels of P<0.05 and P<0.01 using two-tailed Student’s t-test (compared with MPV), respectively.