Fig. 1: CCA1 confers significant heterosis for defense in hybrids.

a Phenotypes of F₁ hybrids and parents 5 dpi with Pst DC3000. Arrows show the leaves inoculated with pathogen. The scale represents 1 cm. b Bacterial titer (log10) of the F₁ hybrids and parents 5 dpi with Pst DC3000 at dawn and at dusk, respectively. c Mid-parent heterosis (MPH) and best-parent heterosis (BPH) values of FCS hybrids calculated by the bacterial number of 5 dpi at dawn and at dusk, respectively. Data are shown as the mean ± SD. Quantitative RT-PCR analysis of the CCA1’s expression level in the F₁ hybrids and parents of Col-0 × Sei-0 (d) and Col-0 × Aa-0 (e) in a 24-h period (12-h light/12-h dark cycles) starting at dawn (ZT0) with Pst DC3000 infiltration. Data are shown as the mean ± SD (n = 3, n indicates biological replicates). Arrows indicate significant upregulation (red) and downregualtion (blue) of CCA1 in F₁ hybrids compared with that in both parents. f Leaf phenotypes of wild-type and CCA1-mutated F₁ hybrids and parents at 5 dpi with Pst DC3000. g Bacterial titer (log10) of the wild-type and CCA1-mutated F₁ hybrids and parents at 5 dpi with Pst DC3000. MPH value (h) and BPH value (i) of wild-type and CCA1-mutated F₁ hybrids calculated by bacterial number at 5 dpi. Data are shown as the mean ± SD. j MPH value of wild-type and CCA1-mutated F₁ hybrids calculated by bacterial number (5 dpi) at dawn and dusk, respectively. Data are shown as the mean ± SD. Bacterial growth in b and g is indicated as the mean values of viable bacteria per gram of leaf tissue ± SD (n = 6, n indicates biological replicates). Both MPH and BPH values of FCS represented by the bacterial number were negative in h–j due to the bacterial number in FCS was significantly less than that in its parents. The results in b–j are representative of three independent experiments, with measurements taken from independent samples grown and processed at different times. dpi: days post infiltration. **p value < 0.01; ***p value < 0.001 (two-tailed Student’s t test).