Arabidopsis AtSPL14, a plant‐specific SBP‐domain transcription factor, participates in plant development and sensitivity to fumonisin B1

Abstract

SummaryThe recessive Arabidopsis thaliana fumonisin B1-resistant (fbr6) mutant was identified by its ability to survive in the presence of a programmed cell death (PCD)-inducing fungal toxin FB1. The fbr6 mutant also displays altered plant architecture in the absence of FB1, most notably elongated petioles and enhanced leaf margin serration. These phenotypes are a result of a T-DNA insertion in the SQUAMOSA promoter binding protein (SBP) domain gene, AtSPL14. AtSPL14 encodes a plant-specific protein with features characteristic of a transcriptional regulator, including a nuclear localization signal sequence, a plant-specific DNA binding domain (the SBP box), and a protein interaction motif (ankyrin repeats). A transiently expressed fusion of the AtSPL14 protein to green fluorescent protein is directed to the plant nucleus. DNA sequences immediately upstream of the translation start site direct expression of the b-glucuronidase reporter gene primarily in the vascular tissues, consistent with the phenotypes of the fbr6 mutant. AtSPL14 activates transcription in yeast, with a transactivation domain residing within the N-terminal region of the protein. Recombinant AtSPL14 protein binds A. thaliana genomic DNA in vitro in the absence of other proteins. These results indicate that FBR6/SPL14 functions as a transcriptional regulator that plays a role not only in sensitivity to FB1, but also in the development of normal plant architecture.

Identification of a Consensus DNA-Binding Site for the Arabidopsis thaliana SBP Domain Transcription Factor, AtSPL14, and Binding Kinetics by Surface Plasmon Resonance

“…FB1 disrupts sphingolipid metabolism in eukaryotes (38) and induces PCD, dependent on transcription, translation, reversible protein phosphorylation, light, and hormone signaling pathways in A. thaliana (10,11). In addition to resistance to FB1, the fbr6 mutant also exhibits altered plant architecture, including elongated petioles and enhanced leaf margin serration (9). Knowledge of the AtSPL14 DNA-binding site (and potentially regulated genes) is critical to fully understanding the physiological functions of this sequence-specific DNA-binding transcription factor.…”

“…To date, only a few functions for SBP domain proteins have been reported, perhaps due to genetic redundancy of closely related family members. In all cases, SBP domain proteins have been implicated in various aspects of plant growth and development, including metal sensing in algae and directing development of leaves, embryos, and floral organs in higher plants (9,(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). Some of these SBP do-main proteins may also be posttranscriptionally regulated by noncoding microRNAs to control their spatial and temporal expression (23)(24)(25).…”

“…Misexpression of the AtSPL14 gene in the fbr6 mutant confers the ability to proliferate in the presence of FB1 and modifies normal plant architecture, linking the insensitivity to cell death to altered plant development (9). AtSPL14 has features of a DNA-binding transcription factor, including a Cys-and His-rich SQUA-MOSA promoter binding protein (SBP) domain predicted to bind DNA, ankyrin repeats that mediate protein-protein interactions, nuclear localization, and ability to bind to A. thaliana genomic DNA (9).…”

“…Despite the essential nature of PCD, large gaps remain in our knowledge of the mechanistic details and molecular components controlling plant PCD. Therefore, to identify novel genes that might participate in plant PCD, we developed a mutant selection scheme for the model plant Arabidopsis thaliana using a PCD-inducing fungal toxin fumonisin B1 (FB1), to identify FB1-resistant (fbr) mutants (9)(10)(11). Misexpression of the AtSPL14 gene in the fbr6 mutant confers the ability to proliferate in the presence of FB1 and modifies normal plant architecture, linking the insensitivity to cell death to altered plant development (9).…”

“…Therefore, to identify novel genes that might participate in plant PCD, we developed a mutant selection scheme for the model plant Arabidopsis thaliana using a PCD-inducing fungal toxin fumonisin B1 (FB1), to identify FB1-resistant (fbr) mutants (9)(10)(11). Misexpression of the AtSPL14 gene in the fbr6 mutant confers the ability to proliferate in the presence of FB1 and modifies normal plant architecture, linking the insensitivity to cell death to altered plant development (9). AtSPL14 has features of a DNA-binding transcription factor, including a Cys-and His-rich SQUA-MOSA promoter binding protein (SBP) domain predicted to bind DNA, ankyrin repeats that mediate protein-protein interactions, nuclear localization, and ability to bind to A. thaliana genomic DNA (9).…”