Abstract
Phytochrome-interacting factors (PIFs) play important roles in photomorphogenesis, the shade avoidance response, and other aspects of plant growth and development. PIF family proteins have been well-studied in Arabidopsis thaliana, but little is known about their physiological functions and molecular mechanisms in maize (Zea mays). In this study, we investigated the physiological functions of ZmPIF4 and ZmPIF5, two highly conserved members of the PIF gene family. RT-qPCR and western blot analyses revealed that ZmPIF4 and ZmPIF5 expression and ZmPIF4 and ZmPIF5 levels peak at night and remain low during the day. Overexpression of ZmPIF4 and ZmPIF5 in Arabidopsis partially rescued the reduced hypocotyl elongation and defective response to gravity in pif1 pif3 pif4 pif5 quadruple mutants (pifq). In addition, under high red: far-red light conditions, Arabidopsis lines overexpressing ZmPIF4 exhibited a constitutive shade avoidance response, including early flowering, slender leaves and inflorescences, plant lodging and precocious leaf senescence. Furthermore, ZmPIF4 physically interacted with the Arabidopsis DELLA protein REPRESSOR OF GA1-3 (RGA), indicating a potential interaction between ZmPIF4 and gibberellin signaling pathway on plant growth. Taken together, our results revealed that ZmPIF4 and ZmPIF5 are functionally conserved proteins that may play conserved roles in the response to phytochrome signaling in plants.Highlights:In this study, the functions of ZmPIF4 and ZmPIF5 were characterized by expression in Arabidopsis, revealing conserved roles of PIF family proteins in photomorphogenesis and the shade avoidance response in land plants.
Highlights
Shade avoidance is mainly triggered by the reduced ratio of R:FR, which is sensed by the phytochrome family of photoreceptors (Franklin et al, 2003; Casal, 2013)
A phylogenetic tree with the protein sequences of Phytochrome-interacting factors (PIFs) family proteins from Arabidopsis and maize showed that the putative ZmPIFs were closely related to AtPIFs (Figure 1A)
Both active phytochrome A binding domains (APA) and active phytochrome B binding domains (APB) domains were identified in the ZmPIF3.1 and ZmPIF3.2, two previously reported PIF family proteins in maize encoded by ZmbHLH76 and ZmbHLH165, respectively (Figure 1B, left lower panel)
Summary
Shade avoidance is mainly triggered by the reduced ratio of R:FR, which is sensed by the phytochrome family of photoreceptors (Franklin et al, 2003; Casal, 2013). The phytochrome family of Arabidopsis thaliana includes five members (phyA–phyE), and phyB is the primarily photoreceptor involved in the shade avoidance response (Franklin et al, 2003; Li et al, 2011). Phytochrome-interacting factors (PIFs) are basic helix-loophelix (bHLH) transcription factors that are involved in seed germination, photomorphogenesis, shade responses, flowering time, and leaf senescence (Leivar and Quail, 2011; Casal, 2013; Sakuraba et al, 2014). Comparison of the protein sequences of PIF family members has shown that they have evolutionarily conserved bHLH domains located at the C-terminal and these domains function in DNA binding and dimer formation. Under low R:FR light conditions, PIFs promotes cell elongation by increasing the transcription of growth-promoting genes (Paik et al, 2017)
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