developed silicon solar cells. It shows the great potential of PSCs as the dominator of next-generation photovoltaics. Whereas, during the evolution of PSC development, the metal oxide electron transporting layer (ETL), as well as the ETL/perovskite interface, [11][12][13][14] has always been an issue in regard to photovoltaic efficiency and device stability. [8] Derived from dye-sensitized solar cells (DSSCs), the combination of compact and mesoporous TiO 2 has been commonly utilized as ETLs during the early studies of PSCs. [15] But a high sintering temperature of ≈500 °C is normally required for the fabrication process, which is high energy consumption and incompatible with scalable depositions on flexible substrates. Worse still, TiO 2 is highly photocatalytic active under ultraviolet (UV) irradiation that severely hampers the long-term stability of PSCs under illumination. [16][17][18][19][20][21][22] Later on, a new ETL, SnO 2 , has been developed as a better candidate, due to its low-temperature processability [23] and high sustainability under UV illumination. [24][25][26][27] More importantly, SnO 2 film has superior crystallinity and carrier mobility in comparison to TiO 2 . [28,29] Thus, a single layer of compact SnO 2 could enable an efficient charge transport and suppressed recombination losses at the ETL/perovskite interface. Benefiting from these advantages, PSCs based on SnO 2 as ETL have reached PCE of 25.2% to date. [30] Whereas, considerable amount of oxygen vacancies on the SnO 2 surface would act as deep traps to capture the photogenerated carriers, which causes hysteresis and instability of the device. [31][32][33][34] And this intrinsic defect of SnO 2 needs to be resolved for a further PCE breakthrough of PSCs.In recent years, significant attempts of defect-passivation have been made to decrease the oxygen vacancies and trap states on SnO 2 surface. [35][36][37][38] Among them, n-type fullerene derivatives represent one of the most studied and efficacious passivator, [39][40][41][42] due to the ease of forming coordinate bonds between carboxylate group and SnO 2 surface. In addition, fullerene derivative is a common electron acceptor in organic solar cells (OSCs), [43] which grants an effective electron extraction from the perovskite active layer to ETL, thus contributing to higher PSC performances. Nevertheless, it should be noticed that π-cage structures of fullerene derivatives are prone to self-aggregate, [44] which strongly affects the validity and SnO 2 has been universally applied as electron transporting layer (ETL) towards the fabrication of highly efficient perovskite solar cells (PSCs), owing to its unique advantages including low-temperature solution-processability, high optical, transmittance and good electrical conductivity. Uncoordinated Sn-dangling bonds on SnO 2 surface exist as deep traps to capture the photogenerated carriers, causing hysteresis and device instability. Fullerene derivatives, though being widely utilized as the passivator for SnO 2 , are highly prone to...

Ubiquitination modulates nearly all aspects of plant life. Here, we reconstituted the Arabidopsis thaliana ubiquitination cascade in Escherichia coli using a synthetic biology approach. In this system, plant proteins are expressed and then immediately participate in ubiquitination reactions within E. coli cells. Additionally, the purification of individual ubiquitination components prior to setting up the ubiquitination reactions is omitted. To establish the reconstituted system, we co-expressed Arabidopsis ubiquitin (Ub) and ubiquitination substrates with E1, E2 and E3 enzymes in E. coli using the Duet expression vectors. The functionality of the system was evaluated by examining the auto-ubiquitination of a RING (really interesting new gene)-type E3 ligase AIP2 and the ubiquitination of its substrate ABI3. Our results demonstrated the fidelity and specificity of this system. In addition, we applied this system to assess a subset of Arabidopsis E2s in Ub chain formation using E2 conjugation assays. Affinity-tagged Ub allowed efficient purification of Ub conjugates in milligram quantities. Consistent with previous reports, distinct roles of various E2s in Ub chain assembly were also observed in this bacterial system. Therefore, this reconstituted system has multiple advantages, and it can be used to screen for targets of E3 ligases or to study plant ubiquitination in detail.