Expression of PHYA-V631M mutant protein is sufficient to cause a dominant interfering effect on endogenous phyA signaling. A, Diagrams of the transformation cassettes. The wild-type PHYA (WT) and PHYA-V631M full-length coding regions were driven by the cauliflower mosaic virus 35S promoter. B, Morphological comparison of 3-d-old FR light-grown seedlings of wild-type PHYA overexpressor (PHYA OE), wild-type (WT), and two mutant PHYA-V631M overexpressor (PHYA-300D OE) lines. PHYA protein immunoblots are shown in the bottom panel. C, Morphological comparison of 3-d-old dark-grown seedlings with PHYA-V631M overexpressor transgene in wild-type background (left) and the wild-type control (right). D, Morphology of 3-d-old FR light-grown seedling with PHYA-V631M overexpressor transgene in a phyA null mutant background. Scale bars in B through D = 1 mm.