Effects of inefficient transcription termination of rbcL on the expression of accD in plastids of Arabidopsis thaliana

The plastid accD gene encodes one subunit of a multimeric acetyl-CoA carboxylase that is required for fatty acid biosynthesis. In Arabidopsis thaliana, the accD gene is transcribed by the nuclear-encoded phage-type RNA polymerase, and the accumulation of accD transcripts is subjected to a dynamic pattern during chloroplast development. However, the mechanisms underlying the regulation of accD expression remain unknown. Here, we showed that the inefficient transcription termination of rbcL due to the absence of RHON1 impaired the developmental profile of accD, resulting in the constitutive expression of accD during chloroplast development. Moreover, the accumulation of accD transcripts accordingly resulted in an increase in accD protein levels, suggesting that transcript abundance is critical for accD gene production. Our study demonstrates that the interplay between accD and upstream rbcL regulates the expression of accD and highlights the significance of transcriptional regulation in plastid gene expression in higher plants

Effects of inefficient transcription termination of rbcL on the expression of accD in plastids of Arabidopsis thaliana

The plastid accD gene encodes one subunit of a multimeric acetyl-CoA carboxylase that is required for fatty acid biosynthesis. In Arabidopsis thaliana, the accD gene is transcribed by the nuclear-encoded phage-type RNA polymerase, and the accumulation of accD transcripts is subjected to a dynamic pattern during chloroplast development. However, the mechanisms underlying the regulation of accD expression remain unknown. Here, we showed that the inefficient transcription termination of rbcL due to the absence of RHON1 impaired the developmental profile of accD, resulting in the constitutive expression of accD during chloroplast development. Moreover, the accumulation of accD transcripts accordingly resulted in an increase in accD protein levels, suggesting that transcript abundance is critical for accD gene production. Our study demonstrates that the interplay between accD and upstream rbcL regulates the expression of accD and highlights the significance of transcriptional regulation in plastid gene expression in higher plants

Plastid sigma factors: Their individual functions and regulation in transcription

AbstractSigma factors are the predominant factors involved in transcription regulation in bacteria. These factors can recruit the core RNA polymerase to promoters with specific DNA sequences and initiate gene transcription. The plastids of higher plants originating from an ancestral cyanobacterial endosymbiont also contain sigma factors that are encoded by a small family of nuclear genes. Although all plastid sigma factors contain sequences conserved in bacterial sigma factors, a considerable number of distinct traits have been acquired during evolution. The present review summarises recent advances concerning the regulation of the structure, function and activity of plastid sigma factors since their discovery nearly 40years ago. We highlight the specialised roles and overlapping redundant functions of plastid sigma factors according to their promoter selectivity. We also focus on the mechanisms that modulate the activity of sigma factors to optimise plastid function in response to developmental cues and environmental signals. This article is part of a Special Issue entitled: Chloroplast Biogenesis

PAB is an assembly chaperone that functions downstream of chaperonin 60 in the assembly of chloroplast ATP synthase coupling factor 1

The chloroplast ATP synthase, a multisubunit complex in the thylakoid membrane, catalyzes the light-driven synthesis of ATP, thereby supplying the energy for carbon fixation during photosynthesis. The chloroplast ATP synthase is composed of both nucleus-and chloroplast-encoded proteins that have required the evolution of novel mechanisms to coordinate the biosynthesis and assembly of chloroplast ATP synthase subunits temporally and spatially. Here we have elucidated the assembly mechanism of the alpha(3)beta(3)gamma core complex of the chloroplast ATP synthase by identification and functional characterization of a key assembly factor, PAB (PROTEIN IN CHLOROPLAST ATPASE BIOGENESIS). PAB directly interacts with the nucleus-encoded gamma subunit and functions downstream of chaperonin 60 (Cpn60)-mediated CF1 gamma subunit folding to promote its assembly into the catalytic core. PAB does not have any recognizable motifs or domains but is conserved in photosynthetic eukaryotes. It is likely that PAB evolved together with the transfer of chloroplast genes into the nucleus to assist nucleus-encoded CF1 gamma assembly into the CF1 core. Such coordination might represent an evolutionarily conserved mechanism for folding and assembly of nucleus-encoded proteins to ensure proper assembly of multiprotein photosynthetic complexes

PAB is an assembly chaperone that functions downstream of chaperonin 60 in the assembly of chloroplast ATP synthase coupling factor 1

The chloroplast ATP synthase, a multisubunit complex in the thylakoid membrane, catalyzes the light-driven synthesis of ATP, thereby supplying the energy for carbon fixation during photosynthesis. The chloroplast ATP synthase is composed of both nucleus- and chloroplast-encoded proteins that have required the evolution of novel mechanisms to coordinate the biosynthesis and assembly of chloroplast ATP synthase subunits temporally and spatially. Here we have elucidated the assembly mechanism of the α(3)β(3)γ core complex of the chloroplast ATP synthase by identification and functional characterization of a key assembly factor, PAB (PROTEIN IN CHLOROPLAST ATPASE BIOGENESIS). PAB directly interacts with the nucleus-encoded γ subunit and functions downstream of chaperonin 60 (Cpn60)-mediated CF(1)γ subunit folding to promote its assembly into the catalytic core. PAB does not have any recognizable motifs or domains but is conserved in photosynthetic eukaryotes. It is likely that PAB evolved together with the transfer of chloroplast genes into the nucleus to assist nucleus-encoded CF(1)γ assembly into the CF(1) core. Such coordination might represent an evolutionarily conserved mechanism for folding and assembly of nucleus-encoded proteins to ensure proper assembly of multiprotein photosynthetic complexes

Investigation on the pollution of road rainwater runoff in Shijiazhuang City

To protect groundwater and urban ecological environment, much more sponge cities have been built in China. The sponge road is an important part of a sponge city. In recent years, Shijiazhuang Municipal Design Institute proposes a new sponge road structure, namely planting soil and crushed stone green belt, and it has been extensively used in Shijiazhuang City. In the design of the road structure, it is a key issue whether the infiltration rainwater quality pollutes the groundwater. Therefore, it is necessary to investigate the pollution of road rainwater runoff in Shijiazhuang City for the design of sponge road and the construction of sponge city. To obtain the characteristics of rainwater runoff pollution in Shijiazhuang City, four investigation points are chosen at the intersection of the Nanerhuan Road and Yuxiang Street, the east gate of Hebei University of Science and Technology, the site under the Xierhuan Road and Zhongshan Road overpass, and the catch-basin along the roadside in Shijiazhuang City. The investigating points are located in the main road of Shijiazhuang urban area, which covers Shijiazhuang City, and can represent the pollution characteristics of road runoff in Shijiazhuang City. Six rainfalls are collected from March to June in 2017. The rainfall on 3, May is viewed as typical middle and light one which is studied in this paper. The concentration of COD, TP, TN, NH3-N and SS in road runoff is tested by potassium dichromate method, ammonium molybdate spectrophotometry, potassium persulfate digestion-UV spectrophotometry and Nessler’s reagent spectrophotometry and filter paper filtration, respectively. The concentrations of Zn ions and Pb ions are tested by inductively coupled plasma method. According to the test results, the concentration evolutions of COD, TP, TN, NH3-N, SS, Zn and Pb ion in runoff during rainfall are studied. The results show that the contaminant concentration approximately decreases during the rainfall, and then maintain stable for 90 min. The relation between contaminant concentration and rainfall time follows the form of negative exponential function. Based on the investigation results, the design values of pollutant concentrations at the initial runoff and the long runoff of rainwater in Shijiazhuang are proposed by time-weighted average method and rainfall-weighted average method, respectively. The recommended values by former method for initial runoff in Shijiazhuang are as follows: TN, NH3-N, TP, SS and COD are 14.49 mg/L, 10.93 mg/L, 0.45 mg/L, 651.00 mg/L and 437.73 mg/L. The recommended values by former method for long runoff of water in Shijiazhuang are as follows: in 90 min TN, NH3-N, TP, SS and COD are 8.05 mg/L, 5.60 mg/L, 0.59 mg/L, 559.22 mg/L, and 237.96 mg/L, respectively. After 90 min they are 5.13 mg/L, 4.11 mg/L, 0.58 mg/L, 422.67 mg/L and 97.35 mg/L. The recommended values by later method for initial runoff in Shijiazhuang are as follows: TN, NH3-N, TP, SS and COD are 14.40 mg/L, 10.86 mg/L, 0.50 mg/L, 684.10 mg/L and 440.08 mg/L. The recommended values by later method for long runoff of water in Shijiazhuang are as follows: in 90 min TN, NH3-N, TP, SS and COD are 12.46 mg/L, 9.19 mg/L, 0. 52 mg/L, 642.80 mg/L and 363.92 mg/L. After 90 min they are 5.13 mg/L, 4.11 mg/L, 0.58 mg/L, 423.30 mg/L and 97.35 mg/L. Overall the proposed concentration values by the rainfall weighted average method are slightly larger than those by the time weighted average method. For hardly degradable Zn and Pb ions in the soil, the 30 min time-weighted concentration at the initial runoff and the long runoff of rainwater is proposed as the design values of runoff rainwater. The recommended design values of Zn and Pb ions are 0.67 mg/L and 0.11 mg/L, respectively

BASIC PENTACYSTEINE Proteins Repress ABSCISIC ACID INSENSITIVE4 Expression via Direct Recruitment of the Polycomb-Repressive Complex 2 in Arabidopsis Root Development

Plant transcription factors generally act in complex regulatory networks that function at multiple levels to govern plant developmental programs. Dissection of the interconnections among different classes of transcription factors can elucidate these regulatory networks and thus improve our understanding of plant development. Here, we investigated the molecular and functional relationships of the transcription factors ABSCISIC ACID INSENSITIVE 4 (ABI4) and members of the BASIC PENTACYSTEINE (BPC) family in lateral root (LR) development of Arabidopsis thaliana. Genetic analysis showed that BPCs promote LR development by repressing ABI4 expression. Molecular analysis showed that BPCs bind to the ABI4 promoter and repress ABI4 transcription in roots. BPCs directly recruit the Polycomb Repressive Complex 2 (PRC2) to the ABI4 locus and epigenetically repress ABI4 expression by catalyzing the trimethylation of histone H3 at Lys27. In addition, BPCs and ABI4 co-ordinate their activities to fine-tune the levels of PIN-FORMED1, a component of the auxin signaling pathway, and thus modulate LR formation. These results establish a functional relationship between two universal and multiple-role transcription factors, and provide insight into the mechanisms of the transcriptional regulatory networks that affect Arabidopsis organogenesis

BASIC PENTACYSTEINE Proteins Repress ABSCISIC ACID INSENSITIVE4 Expression via Direct Recruitment of the Polycomb-Repressive Complex 2 in Arabidopsis Root Development.

Plant transcription factors generally act in complex regulatory networks that function at multiple levels to govern plant developmental programs. Dissection of the interconnections among different classes of transcription factors can elucidate these regulatory networks and thus improve our understanding of plant development. Here, we investigated the molecular and functional relationships of the transcription factors ABSCISIC ACID INSENSITIVE 4 (ABI4) and members of the BASIC PENTACYSTEINE (BPC) family in lateral root (LR) development of Arabidopsis thaliana. Genetic analysis showed that BPCs promote LR development by repressing ABI4 expression. Molecular analysis showed that BPCs bind to the ABI4 promoter and repress ABI4 transcription in roots. BPCs directly recruit the Polycomb Repressive Complex 2 (PRC2) to the ABI4 locus and epigenetically repress ABI4 expression by catalyzing the trimethylation of histone H3 at Lys27. In addition, BPCs and ABI4 co-ordinate their activities to fine-tune the levels of PIN-FORMED1, a component of the auxin signaling pathway, and thus modulate LR formation. These results establish a functional relationship between two universal and multiple-role transcription factors, and provide insight into the mechanisms of the transcriptional regulatory networks that affect Arabidopsis organogenesis