Arabidopsis Forkhead-Associated Domain Protein 3 negatively regulates peroxisome division.

Peroxisomes are ubiquitous and dynamic eukaryotic organelles capable of altering their abundance in response to environmental and developmental cues, yet the regulatory mechanism of plant peroxisome division/proliferation is unclear. To identify transcriptional regulators of the peroxisome division factor gene PEX11b, we performed a nuclear pull-down experiment and identified Arabidopsis Forkhead-Associated Domain Protein 3 (FHA3) as a novel protein that binds to the promoter of PEX11b. Our data supported the conclusion that, in contrast to the previously identified HY5 HOMOLOG (HYH) protein that promotes the transcription of PEX11b, FHA3 is a negative regulator of PEX11b expression and peroxisome division.

Ectopic expression of the RING domain of the Arabidopsis peroxin2 protein partially suppresses the phenotype of the photomorphogenic mutant de-etiolated1.

The Arabidopsis constitutive photomorphogenic/de-etiolated 1/FUSCA (COP/DET1/FUS) proteins repress photomorphogenesis by degrading positive regulators of photomorphogenesis, such as the transcription factor long hypocotyl5 (HY5). The gain-of-function mutant ted3, which partially suppresses the det1 mutant, contains a missense mutation of a Val-to-Met substitution before the C-terminal RING finger domain of the peroxisomal membrane protein peroxin2 (PEX2). We hypothesized that a truncated PEX2 protein, which only contains the C-terminal RING domain, is initiated by the ted3 mutation and by-passes the function of DET1 in the nucleus.

Two inositol hexakisphosphate kinases drive inositol pyrophosphate synthesis in plants.

Inositol pyrophosphates are unique cellular signaling molecules with recently discovered roles in energy sensing and metabolism. Studies in eukaryotes have revealed that these compounds have a rapid turnover, and thus only small amounts accumulate. Inositol pyrophosphates have not been the subject of investigation in plants even though seeds produce large amounts of their precursor, myo-inositol hexakisphosphate (InsP6 ).

A role for lipid-mediated signaling in plant gravitropism.

Gravitropism is a universal plant response. It is initiated by the sensing of the primary signal (mass or pressure), which is then converted into chemical signals that are transduced and propagated in a precise spatial and temporal fashion, resulting in a differential growth response. Our thesis is that membrane lipids and lipid-mediated signaling pathways play critical roles in the initial signaling and in the establishment of polarity.

Light control of peroxisome proliferation during Arabidopsis photomorphogenesis.

Peroxisomes are multifunctional organelles whose abundance and metabolic activities differ depending on the species, cell type, developmental stage and prevailing environmental conditions.1 However, little is known about the signaling pathways that control these variations, especially in plants. Our laboratory recently investigated the regulatory role of light in changes in peroxisome abundance and identified a phytochrome A-dependent pathway responsible for the proliferation of peroxisomes during dark-to-light transition in Arabidopsis seedlings.

LZF1/SALT TOLERANCE HOMOLOG3, an Arabidopsis B-box protein involved in light-dependent development and gene expression, undergoes COP1-mediated ubiquitination.

B-box containing proteins play an important role in light signaling in plants. Here, we identify LIGHT-REGULATED ZINC FINGER1/SALT TOLERANCE HOMOLOG3 (STH3), a B-box encoding gene that genetically interacts with two key regulators of light signaling, ELONGATED HYPOCOTYL5 (HY5) and CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1). STH3 physically interacts with HY5 in vivo and shows a COP1-dependent localization to nuclear speckles when coexpressed with COP1 in plant cells.

Light induces peroxisome proliferation in Arabidopsis seedlings through the photoreceptor phytochrome A, the transcription factor HY5 HOMOLOG, and the peroxisomal protein PEROXIN11b.

Peroxisomes are single membrane-delimited subcellular organelles that carry out numerous vital metabolic reactions in nearly all eukaryotes. Peroxisomes alter their morphology, abundance, and enzymatic constituents in response to environmental cues, yet little is known about the underlying mechanisms. In this work, we investigated the regulatory role of light in peroxisome proliferation in Arabidopsis (Arabidopsis thaliana).