The AGL6-ELF3-FT circuit controls flowering time in Arabidopsis.

Adjusting the timing of floral transition is essential for reproductive success in plants. A number of flowering regulators integrate internal and external signals to precisely determine the time to flower. We here report that the AGAMOUS-LIKE 6 (AGL6) - EARLY FLOWERING 3 (ELF3) module regulates flowering in the FLOWERING LOCUS T (FT)-dependent pathway in Arabidopsis. The AGL6 transcriptional repressor promotes floral transition by directly suppressing ELF3, which in turn directly represses FT expression that acts as a floral integrator. Indeed, ELF3 is epistatic to AGL6 in the control of floral transition. Overall, our findings propose that the AGL6-ELF3 module contributes to fine-tuning flowering time in plants.

ESR2-HDA6 complex negatively regulates auxin biosynthesis to delay callus initiation in Arabidopsis leaf explants during tissue culture.

Plants exhibit an astonishing ability to regulate organ regeneration upon wounding. Excision of leaf explants promotes the biosynthesis of indole-3-acetic acid (IAA), which is polar-transported to excised regions, where cell fate transition leads to root founder cell specification to induce de novo root regeneration. The regeneration capacity of plants has been utilized to develop in vitro tissue culture technologies. Here, we report that IAA accumulation near the wounded site of leaf explants is essential for callus formation on 2,4-dichlorophenoxyacetic acid (2,4-D)-rich callus-inducing medium (CIM). Notably, a high concentration of 2,4-D does not compensate for the action of IAA because of its limited efflux; rather, it lowers IAA biosynthesis via a negative feedback mechanism at an early stage of in vitro tissue culture, delaying callus initiation. The auxin negative feedback loop in CIM-cultured leaf explants is mediated by an auxin-inducible APETALA2 transcription factor, ENHANCER OF SHOOT REGENERATION 2 (ESR2), along with its interacting partner HISTONE DEACETYLASE 6 (HDA6). The ESR2-HDA6 complex binds directly to, and removes the H3ac mark from, the YUCCA1 (YUC1), YUC7, and YUC9 loci, consequently repressing auxin biosynthesis and inhibiting cell fate transition on 2,4-D-rich CIM. These findings indicate that negative feedback regulation of auxin biosynthesis by ESR2 and HDA6 interferes with proper cell fate transition and callus initiation.

ENHANCER OF SHOOT REGENERATION1 promotes de novo root organogenesis after wounding in Arabidopsis leaf explants.

Plants have an astonishing ability to regenerate new organs after wounding. Here, we report that the wound-inducible transcription factor ENHANCER OF SHOOT REGENERATION1 (ESR1) has a dual mode of action in activating ANTHRANILATE SYNTHASE ALPHA SUBUNIT1 (ASA1) expression to ensure auxin-dependent de novo root organogenesis locally at wound sites of Arabidopsis (Arabidopsis thaliana) leaf explants. In the first mode, ESR1 interacts with HISTONE DEACETYLASE6 (HDA6), and the ESR1-HDA6 complex directly binds to the JASMONATE-ZIM DOMAIN5 (JAZ5) locus, inhibiting JAZ5 expression through histone H3 deacetylation. As JAZ5 interferes with the action of ETHYLENE RESPONSE FACTOR109 (ERF109), the transcriptional repression of JAZ5 at the wound site allows ERF109 to activate ASA1 expression. In the second mode, the ESR1 transcriptional activator directly binds to the ASA1 promoter to enhance its expression. Overall, our findings indicate that the dual biochemical function of ESR1, which specifically occurs near wound sites of leaf explants, maximizes local auxin biosynthesis and de novo root organogenesis in Arabidopsis.

Overexpression of OsERF83, a Vascular Tissue-Specific Transcription Factor Gene, Confers Drought Tolerance in Rice.

Abiotic stresses severely affect plant growth and productivity. To cope with abiotic stresses, plants have evolved tolerance mechanisms that are tightly regulated by reprogramming transcription factors (TFs). APETALA2/ethylene-responsive factor (AP2/ERF) transcription factors are known to play an important role in various abiotic stresses. However, our understanding of the molecular mechanisms remains incomplete. In this study, we identified the role of OsERF83, a member of the AP2/ERF transcription factor family, in response to drought stress. OsERF83 is a transcription factor localized to the nucleus and induced in response to various abiotic stresses, such as drought and abscisic acid (ABA). Overexpression of OsERF83 in transgenic plants (OsERF83OX) significantly increased drought tolerance, with higher photochemical efficiency in rice. OsERF83OX was also associated with growth retardation, with reduced grain yields under normal growth conditions. OsERF83 is predominantly expressed in the vascular tissue of all organs. Transcriptome analysis revealed that OsERF83 regulates drought response genes, which are related to the transporter (OsNPF8.10, OsNPF8.17, OsLH1), lignin biosynthesis (OsLAC17, OsLAC10, CAD8D), terpenoid synthesis (OsTPS33, OsTPS14, OsTPS3), cytochrome P450 family (Oscyp71Z4, CYP76M10), and abiotic stress-related genes (OsSAP, OsLEA14, PCC13-62). OsERF83 also up-regulates biotic stress-associated genes, including PATHOGENESIS-RELATED PROTEIN (PR), WALL-ASSOCIATED KINASE (WAK), CELLULOSE SYNTHASE-LIKE PROTEIN E1 (CslE1), and LYSM RECEPTOR-LIKE KINASE (RLK) genes. Our results provide new insight into the multiple roles of OsERF83 in the cross-talk between abiotic and biotic stress signaling pathways.