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1.  A Competitive Peptide Inhibitor KIDARI Negatively Regulates HFR1 by Forming Nonfunctional Heterodimers in Arabidopsis Photomorphogenesis 
Molecules and Cells  2012;35(1):25-31.
Dynamic dimer formation is an elaborate means of modulating transcription factor activities in diverse cellular processes. The basic helix-loop-helix (bHLH) transcription factor LONG HYPOCOTYL IN FAR-RED 1 (HFR1), for example, plays a role in plant photomorphogenesis by forming non-DNA binding heterodimers with PHYTOCHROME-INTERACTING FACTORS (PIFs). Recent studies have shown that a small HLH protein KIDARI (KDR) negatively regulates the HFR1 activity in the process. However, molecular mechanisms underlying the KDR control of the HFR1 activity are unknown. Here, we demonstrate that KDR attenuates the HFR1 activity by competitively forming nonfunctional heterodimers, causing liberation of PIF4 from the transcriptionally inactive HFR1-PIF4 complex. Accordingly, the photomorphogenic hypocotyl growth of the HFR1-overexpres-sing plants can be suppressed by KDR coexpression, as observed in the HFR1-deficient hfr1-201 mutant. These results indicate that the PIF4 activity is modulated through a double layer of competitive inhibition by HFR1 and KDR, which could in turn ensure fine-tuning of the PIF4 activity under fluctuating light conditions.
PMCID: PMC3887847  PMID: 23224238
Arabidopsis; competitive inhibition; KIDARI (KDR); light signaling; LONG HYPOCOTYL IN FAR-RED 1 (HFR1); PHYTOCHROME-INTERACTING FACTOR (PIF)
2.  Molecular and functional characterization of cold-responsive C-repeat binding factors from Brachypodium distachyon 
BMC Plant Biology  2014;14:15.
Adverse environmental conditions severely influence various aspects of plant growth and developmental processes, causing worldwide reduction of crop yields. The C-repeat binding factors (CBFs) are critical transcription factors constituting the gene regulatory network that mediates the acclimation process to low temperatures. They regulate a large number of cold-responsive genes, including COLD-REGULATED (COR) genes, via the CBF-COR regulon. Recent studies have shown that the CBF transcription factors also play a role in plant responses to drought and salt stresses. Putative CBF gene homologues and their downstream genes are also present in the genome of Brachypodium distachyon, which is perceived as a monocot model in recent years. However, they have not been functionally characterized at the molecular level.
Three CBF genes that are responsive to cold were identified from Brachypodium, designated BdCBF1, BdCBF2, and BdCBF3, and they were functionally characterized by molecular biological and transgenic approaches in Brachypodium and Arabidopsis thaliana. Our results demonstrate that the BdCBF genes contribute to the tolerance response of Brachypodium to cold, drought, and salt stresses by regulating downstream targets, such as DEHYDRIN5.1 (Dhn5.1) and COR genes. The BdCBF genes are induced under the environmental stress conditions. The BdCBF proteins possess transcriptional activation activity and bind directly to the promoters of the target genes. Transgenic Brachypodium plants overexpressing the BdCBF genes exhibited enhanced resistance to drought and salt stresses as well as low temperatures, and accordingly endogenous contents of proline and soluble sugars were significantly elevated in the transgenic plants. The BdCBF transcription factors are also functional in the heterologous system Arabidopsis. Transgenic Arabidopsis plants overexpressing the BdCBF genes were also tolerant to freezing, drought, and salt stresses, and a set of stress-responsive genes was upregulated in the transgenic Arabidopsis plants.
Taken together, our results strongly support that the BdCBF transcription factors are key regulators of cold stress responses in Brachypodium and the CBF-mediated cold stress signaling pathway is conserved in this plant species. We believe that this study would confer great impact on stress biology in monocot species and could be applied to engineer abiotic stress tolerance of bioenergy grass species.
PMCID: PMC3898008  PMID: 24405987
Brachypodium distachyon; C-repeat binding factor (CBF); COLD-REGULATED (COR); Abiotic stress tolerance; Arabidopsis thaliana
3.  The Floral Repressor BROTHER OF FT AND TFL1 (BFT) Modulates Flowering Initiation under High Salinity in Arabidopsis 
Molecules and Cells  2011;32(3):295-303.
Floral transition is coordinately regulated by both endogenous and exogenous cues to ensure reproductive success under fluctuating environmental conditions. Abiotic stress conditions, including drought and high salinity, also have considerable influence on this developmental process. However, the signaling components and molecular mechanisms underlying the regulation of floral transition by environmental factors have not yet been defined. In this work, we show that the Arabidopsis BROTHER OF FT AND TFL1 (BFT) gene, which encodes a member of the FLOWERING LOCUS T (FT)/TERMINAL FLOWER 1 (TFL1) family, regulates floral transition under conditions of high salinity. The BFT gene was transcriptionally induced by high salinity in an abscisic acid (ABA)-dependent manner. Transgenic plants overexpressing the BFT gene (35S:BFT) and BFT-deficient mutant (bft-2) plants were phenotypically indistinguishable from Col-0 plants in seed germination and seedling growth under high salinity. In contrast, although the floral transition was delayed significantly in Col-0 plants under high salinity, that of the bft-2 mutant was not affected by high salinity. We also observed that expression of the APETALA1 (AP1) gene was suppressed to a lesser degree in the bft-2 mutant than in Col-0 plants. Taken together, our observations suggest that BFT mediates salt stress-responsive flowering, providing an adaptive strategy that ensures reproductive success under unfavorable stress conditions.
PMCID: PMC3887636  PMID: 21809215
abscisic acid; Arabidopsis; BFT; flowering; salt stress
4.  Identification and characterization of circadian clock genes in a native tobacco, Nicotiana attenuata 
BMC Plant Biology  2012;12:172.
A plant’s endogenous clock (circadian clock) entrains physiological processes to light/dark and temperature cycles. Forward and reverse genetic approaches in Arabidopsis have revealed the mechanisms of the circadian clock and its components in the genome. Similar approaches have been used to characterize conserved clock elements in several plant species. A wild tobacco, Nicotiana attenuata has been studied extensively to understand responses to biotic or abiotic stress in the glasshouse and also in their native habitat. During two decades of field experiment, we observed several diurnal rhythmic traits of N. attenuata in nature. To expand our knowledge of circadian clock function into the entrainment of traits important for ecological processes, we here report three core clock components in N. attenuata.
Protein similarity and transcript accumulation allowed us to isolate orthologous genes of the core circadian clock components, LATE ELONGATED HYPOCOTYL (LHY), TIMING OF CAB EXPRESSION 1/PSEUDO-RESPONSE REGULATOR 1 (TOC1/PRR1), and ZEITLUPE (ZTL). Transcript accumulation of NaLHY peaked at dawn and NaTOC1 peaked at dusk in plants grown under long day conditions. Ectopic expression of NaLHY and NaZTL in Arabidopsis resulted in elongated hypocotyl and late-flowering phenotypes. Protein interactions between NaTOC1 and NaZTL were confirmed by yeast two-hybrid assays. Finally, when NaTOC1 was silenced in N. attenuata, late-flowering phenotypes under long day conditions were clearly observed.
We identified three core circadian clock genes in N. attenuata and demonstrated the functional and biochemical conservation of NaLHY, NaTOC1, and NaZTL.
PMCID: PMC3489836  PMID: 23006446
Circadian clock; Flowering time; NaLHY; NaTOC1; NaZTL; Nicotiana attenuata; Protein interaction

Results 1-4 (4)