Summary The changing environments strongly affect plants growth and development. Phytohormones, endogenous plant-made small molecules such as ethylene, regulate a wide range of processes throughout the lifetime of plants[1, 2]. The ability of plants to integrate external signals with endogenous regulatory pathways is vital for their survival [3, 4]. Ethylene was found to suppress hypocotyl elongation in darkness[5], while promote it in light[6, 7]. How ethylene regulates hypocotyl elongation in such an opposite way is largely unknown. In particular, how light modulates and even reverses the function of ethylene has yet to be characterized. Here we show that the bHLH transcription factor Phytochrome-Interacting Factor 3 (PIF3), is directly activated by Ethylene-Insensitive 3 (EIN3), and is indispensible for ethylene-induced hypocotyl elongation in light. Ethylene via EIN3 concomitantly activates two contrasting pathways: the PIF3-dependent growth-promoting pathway and an Ethylene-Response Factor 1 (ERF1)-mediated growth-inhibiting pathway. The PIF3 pathway is saturated in dark but progressively fortified with light de-stabilizing PIF proteins to reduce their redundancy. While the ERF1 pathway is mainly functional in dark but gradually saturated with light dramatically stabilizing ERF1 protein. Our findings provide a mechanistic insight into how light modulates internal hormone-regulated plant growth.

Summary The survival of seed plants in natural environments requires the successful emergence from the soil. In this process, the ethylene signaling pathway is utilized by plants to sense and respond to the mechanical resistance of the soil. Here, we report that CONSTITUTIVE PHOTOMORPHOGENESIS 1 (COP1), a central repressor of light signaling, is a key component required for seedlings to sense the depth of soil overlay. Mutation in COP1 causes severe defects in penetrating soil, due to decreased level of EIN3, a master transcription factor in ethylene pathway that mediates seedling emergence. We show that COP1 directly targets the F-box proteins EBF1 and EBF2 for ubiquitination and degradation, thus stabilizing EIN3. As seedlings grow towards the surface, the depth of soil overlay decreases, resulting in a gradual increase of light fluences. COP1 channels the light signals while ethylene transduces the information on soil mechanical conditions, which cooperatively control EIN3 protein levels to promote seedling emergence from the soil. The COP1-EBF1/2-EIN3 module reveals a mechanism by which plants sense the depth to surface and uncovers a novel regulatory paradigm of an ubiquitin E3 ligase cascade.

Significance Seedlings’ ability to both adapt to their soil environment and acquire photoautotrophic capacity under various buried conditions is a life-or-death issue for terrestrial flowering plants. By designing and utilizing a standardized real-soil assay, we identify the key features of germinating seedlings’ soil response and deduce that the gaseous phytohormone ethylene acts as the primary regulator of soil-induced plant morphogenetic changes. Moreover, our study illustrates that an EIN3/EIL1-conducted PIF3–ERF1 molecular circuitry enables seedlings to synchronize the rate of protochlorophyllide biosynthesis with upward growth, a mechanism critical to the prevention of photooxidative damage during seedlings’ initial transition from dark to light in natural conditions.

Summary Plants germinating under subterranean darkness assume skotomorphogenesis, a developmental program strengthened by ethylene in response to mechanical pressure of soil. Upon reaching the surface, light triggers a dramatic developmental transition termed de-etiolation that requires immediate termination of ethylene responses. Here, we report that light-activation of photoreceptor phyB results in rapid degradation of EIN3, the master transcription factor in ethylene signaling pathway. As a result, light rapidly and efficiently represses ethylene actions. Specifically, phyB directly interacts with EIN3 in a light-dependent manner and also physically associates with F-box protein EBFs. The light-activated association of phyB, EIN3, and EBF1/EBF2 proteins stimulates robust EIN3 degradation by SCFEBF1/EBF2 E3 ligases. We reveal that phyB manipulates substrate-E3 ligase interactions in a light-dependent manner, thus directly controlling the stability of EIN3. Our findings illustrate a mechanistic model of how plants transduce the light information to immediately turn off ethylene signaling for de-etiolation initiation.

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It is crucial to deliver anticancer drugs to target cells with high precision and efficiency. While nanomaterials have been shown to enhance the delivery efficiency once they reach the target, it remains challenging for precise drug delivery to overcome the nonspecific adsorption and off-target effect. To meet this challenge, we report herein the design of a novel DNA nanostructure to act as a DNA nanoscale precision-guided missile (D-PGM) for highly efficient loading and precise delivery of chemotherapeutic agents to specific target cells. The D-PGM consists of two parts: a warhead (WH) and a guidance/control (GC). The WH is a rod-like DNA nanostructure as a drug carrier, whose trunk is a three-dimensionally self-assembled DNA nanoscale architecture from the programmed hybridization among two palindromic DNA sequences in the x−y dimension and two common DNA oligonucleotides in the z direction, making the WH possess a high payload capacity of drugs. The GC is an aptamer-based logic gate assembled in a highly organized fashion capable of performing cell-subtype-specific recognition via the sequential disassembly, mediated by cell-anchored aptamers. Because of the cooperative effects between the WH and the GC, the GC logic gates operate like the guidance and control system in a precisionguided missile to steer the doxorubicin (DOX)-loaded DNA WH toward target cancer cells, leading to selective and enhanced therapeutic efficacy. Moreover, fluorophores attached to different locations of D-PGM and DOX fluorescence dequenching upon release enable intracellular tracing of the DNA nanostructures and drugs. The results demonstrate that by mimicking the functionalities of a military precision-guided missile to design the sequential disassembly of the GC system in multistimuli-responsive fashion, our intrinsically biocompatible and degradable D-PGM can accurately identify target cancer cells in complex biological milieu and achieve active targeted drug delivery. The success of this strategy paves the way for specific cell identity and targeted cancer therapy.

DNA is a highly programmable material that can be configured into unique high-order structures, such as DNA branched junctions containing multiple helical arms converging at a center. Herein we show that DNA programmability can deliver in situ growth of a 3-way junction-based DNA structure (denoted Y-shaped DNA) with the use of three hairpin-shaped DNA molecules as precursors, a specific microRNA target as a recyclable trigger, and a DNA polymerase as a driver. We demonstrate that the Y-shaped configuration comes with the benefit of restricted freedom of movement in confined cellular environment, which makes the approach ideally suited for in situ imaging of small RNA targets, such as microRNAs. Comparative analysis illustrates that the proposed imaging technique is superior to both the classic fluorescence in situ hybridization (FISH) method and an analogous amplified imaging method via programmed growth of a double-stranded DNA (rather than Y-shaped DNA) product.

DNA nanostructures have shown potential in cancer therapy. However, their clinical application is hampered by the difficulty to deliver them into cancer cells and susceptibility to nuclease degradation. To overcome these limitations, we report herein a periodically ordered nick‐hidden DNA nanowire (NW) with high serum stability and active targeting functionality. The inner core is made of multiple connected DNA double helices, and the outer shell is composed of regularly arranged standing‐up hairpin aptamers. All termini of the components are hidden from nuclease attack, whereas the target‐binding sites are exposed to allow delivery to the cancer target. The DNA NW remained intact during incubation for 24 h in serum solution. Animal imaging and cell apoptosis showed that NWs loaded with an anticancer drug displayed long blood‐circulation time and high specificity in inducing cancer‐cell apoptosis, thus validating this approach for the targeted imaging and therapy of cancers.