Abstract
Phytochrome A is the primary photoreceptor for mediating various far-red light-induced responses in higher plants. We recently showed that Arabidopsis (Arabidopsis thaliana) FAR-RED ELONGATED HYPOCOTYL3 (FHY3) and FAR-RED-IMPAIRED RESPONSE1 (FAR1), a pair of homologous proteins sharing significant sequence homology to Mutator-like transposases, act as novel transcription factors essential for activating the expression of FHY1 and FHL (for FHY1-like), whose products are required for light-induced phytochrome A nuclear accumulation and subsequent light responses. FHY3, FAR1, and Mutator-like transposases also share a similar domain structure, including an N-terminal C2H2 zinc finger domain, a central putative core transposase domain, and a C-terminal SWIM motif (named after SWI2/SNF and MuDR transposases). In this study, we performed a promoter-swapping analysis of FHY3 and FAR1. Our results suggest that the partially overlapping functions of FHY3 and FAR1 entail divergence of their promoter activities and protein subfunctionalization. To gain a better understanding of the molecular mode of FHY3 function, we performed a structure-function analysis, using site-directed mutagenesis and transgenic approaches. We show that the conserved N-terminal C2H2 zinc finger domain is essential for direct DNA binding and biological function of FHY3 in mediating light signaling, whereas the central core transposase domain and C-terminal SWIM domain are essential for the transcriptional regulatory activity of FHY3 and its homodimerization or heterodimerization with FAR1. Furthermore, the ability to form homodimers or heterodimers largely correlates with the transcriptional regulatory activity of FHY3 in plant cells. Together, our results reveal discrete roles of the multiple domains of FHY3 and provide functional support for the proposition that FHY3 and FAR1 represent transcription factors derived from a Mutator-like transposase(s).
Highlights
Phytochrome A is the primary photoreceptor for mediating various far-red light-induced responses in higher plants
Among all phyA signaling mutants identified so far, the phenotypes of fhy3 and fhy1 mutants most closely resemble that of the phyA photoreceptor mutant, and it has been suggested that FAR-RED ELONGATED HYPOCOTYL3 (FHY3) and FHY1 act early and close to the photoreceptor itself (Desnos et al, 2001; Wang and Deng, 2002; Wang et al, 2002)
Despite their relatively ancient divergence in evolution, the similar yet distinct phenotypes displayed by loss-of-function fhy3 and far1 mutants suggest that FHY3 and FAR-REDIMPAIRED RESPONSE1 (FAR1) likely play partially overlapping functions in phyA signaling
Summary
Phytochrome A is the primary photoreceptor for mediating various far-red light-induced responses in higher plants. FHY3, FAR1, and Mutator-like transposases share a similar domain structure, including an N-terminal C2H2 zinc finger domain, a central putative core transposase domain, and a C-terminal SWIM motif (named after SWI2/SNF and MuDR transposases). We show that the conserved N-terminal C2H2 zinc finger domain is essential for direct DNA binding and biological function of FHY3 in mediating light signaling, whereas the central core transposase domain and C-terminal SWIM domain are essential for the transcriptional regulatory activity of FHY3 and its homodimerization or heterodimerization with FAR1. FHY3, FAR1, and Mutator-like transposases share a similar domain structure, including an N-terminal C2H2 zinc finger domain, a central putative core transposase domain, and a C-terminal SWIM motif (named after SWI2/SNF and MuDR transposases; Makarova et al, 2002). Our results provide functional support for the proposition that FHY3 and FAR1 define a novel class of transcription factors derived from an ancient Mutator-like transposase(s)
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