To understand the functional significance of RNA processing for the expression of plastome-encoded photosynthesis genes, we investigated the nuclear mutation hcf107 of Arabidopsis. The mutation is represented by two alleles, both of which lead to a defective photosystem II (PSII). In vivo protein labeling, in vitro phosphorylation, and immunoblot experiments revealed that the psbB gene product (CP47) and an 8-kD phosphoprotein, the psbH gene product (PsbH), are absent in mutant plants. PsbH and PsbB are essential requirements for PSII assembly in photosynthetic eukaryotes, and their absence in hcf107 is consistent with the PSII-less mutant phenotype. RNA gel blot hybridizations showed that the hcf107 mutation specifically impairs the accumulation of some but not all oligocistronic psbH transcripts that are released from the pentacistronic psbB-psbT-psbH-petB-petD precursor RNA by intergenic endonucleolytic cleavage. In contrast, neither the levels nor the sizes of psbB-containing RNAs are affected. S1 nuclease protection analyses revealed that psbH RNAs are lacking only where psbH is the leading cistron and that they are processed at position -45 in the 5' leader segment of psbH. These data and additional experiments with the cytochrome b(6)f complex mutant hcf152, which is defective in 3' psbH processing, suggest that only those psbH-containing transcripts that are processed at their -45 5' ends can be translated. Secondary structure analysis of the 5' psbH leader predicted the formation of stable stem loops in the nonprocessed transcripts, which are unfolded by processing at the -45 site. We propose that this unfolding of the psbH leader segment as a result of RNA processing is essential for the translation of the psbH reading frame. We suggest further that HCF107 has dual functions: it is involved in intercistronic processing of the psbH 5' untranslated region or the stabilization of 5' processed psbH RNAs, and concomitantly, it is required for the synthesis of CP47.
Abscission is a process that involves shedding of plant organs from the main plant body. In this study it is shown that the process of petal separation in the fragrant rose, Rosa bourboniana, is accompanied by the expression of two xyloglucan endotransglucosylase/hydrolase genes, RbXTH1 and RbXTH2. The sequences of the two genes show 52% amino acid identity but are conserved at the catalytic site. The genes are up-regulated soon after the initiation of the abscission process and their transcription is associated with the progression of abscission, being faster in ethylene-treated flowers but slower during field abscission. Transcription is ethylene responsive, with the ethylene response being tissue-specific for RbXTH1 but largely tissue-independent for RbXTH2. Expression is correlated with an increase in xyloglucan endotransglucosylase (XET) action in petal abscission zones of both ethylene-treated and field abscising flowers. Proximal promoters of both the genes drive β-glucuronidase expression in an ethylene-responsive and abscission-related manner in agrobacteria-infiltrated rose petals, indicating that cis-elements governing ethylene-responsive and abscission-related expression probably lie within the first 700 nucleotides upstream of the translational initiation codon. The results show that cell wall remodelling of the xyloglucan moieties through the XET action of XTHs may be important for cell separation during abscission.
zThese authors contributed equally to this work.
SummaryAn Arabidopsis mutant that exhibited reduced root length was isolated from a population of activationtagged T-DNA insertion lines in a screen for aberrant root growth. This mutant also exhibited reduced hypocotyl length as well as a delay in greening and altered leaf shape. Molecular genetic analysis of the mutant indicated a single T-DNA insertion in the gene RpoT;2 encoding a homolog of the phage-type RNA polymerase (RNAP), that is targeted to both mitochondria and plastids. A second T-DNA-tagged allele also showed a similar phenotype. The mutation in RpoT;2 affected the light-induced accumulation of several plastid mRNAs and proteins and resulted in a lower photosynthetic ef®ciency. In contrast to the alterations in the plastid gene expression, no major effect of the rpoT;2 mutation on the accumulation of examined mitochondrial gene transcripts and proteins was observed. The rpoT;2 mutant exhibited tissue-speci®c alterations in the transcript levels of two other organelle-directed nuclear-encoded RNAPs, RpoT;1 and RpoT;3. This suggests the existence of cross-talk between the regulatory pathways of the three RNAPs through organelle to nucleus communication. These data provide an important information on a role of RpoT;2 in plastid gene expression and early plant development.
SummaryExpression of the genes of plastidial psbB operon (psbB-psbT-psbH-petB-petD) involves multiple processing events and formation of several mono-, di-and multi-cistronic transcripts which are further regulated by differential stability and expression. Here we describe the identification of the HCF107 gene that is involved in the 5¢-end processing/stability and/or translation of the psbH gene and in the translation of the psbB gene. HCF107 is an RNA-TPR-containing protein with 11 RTPRs that are tandemly arranged. A single mutation in the third RTPR that changes a conserved alanine residue to a threonine affects both 5¢-end-processed psbH transcript accumulation as well as psbB translation, resulting in disruption of PSII and seedling lethal plants. The protein is localized to the plastid membranes and is present as part of a multi-subunit complex in the range of 60-190 and 600-800 kDa. HCF107 thus represents a new member of the growing helical repeat family of proteins that seem to play a gene-specific role in regulating plastidial gene expression and biogenesis.
The AP2 domain class of transcription factors is a large family of genes with various roles in plant development and adaptation but with very little functional information in plants other than Arabidopsis. Here, the characterization of an EAR motif-containing transcription factor, SlERF36, from tomato that affects stomatal density, conductance, and photosynthesis is described. Heterologous expression of SlERF36 under the CaMV35S promoter in tobacco leads to a 25–35% reduction in stomatal density but without any effect on stomatal size or sensitivity. Reduction in stomatal density leads to a marked reduction in stomatal conductance (42–56%) as well as transpiration and is associated with reduced CO2 assimilation rates, reduction in growth, early flowering, and senescence. A prominent adaptive response of SlERF36 overexpressors is development of constitutively high non-photochemical quenching (NPQ) that might function as a protective measure to prevent damage from high excitation pressure. The high NPQ leads to markedly reduced light utilization and low electron transport rates even at low light intensities. Taken together, these data suggest that SlERF36 exerts a negative control over stomatal density and modulates photosynthesis and plant development through its direct or indirect effects.
Chickpea (C. arietinum L.) is an important pulse crop in Asian and African countries that suffers significant yield losses due to attacks by insects like H. armigera. To obtain insights into early responses of chickpea to insect attack, a transcriptomic analysis of chickpea leaves just 20 minutes after simulated herbivory was performed, using oral secretions of H. armigera coupled with mechanical wounding. Expression profiles revealed differential regulation of 8.4% of the total leaf transcriptome with 1334 genes up-regulated and 501 down-regulated upon wounding at log2-fold change (|FC| ≤ −1 and ≥1) and FDR value ≤ 0.05. In silico analysis showed the activation of defenses through up-regulation of genes of the phenylpropanoid pathway, pathogenesis, oxidases and CYTP450 besides differential regulation of kinases, phosphatases and transcription factors of the WRKY, MYB, ERFs, bZIP families. A substantial change in the regulation of hormonal networks was observed with up-regulation of JA and ethylene pathways and suppression of growth associated hormone pathways like GA and auxin within 20 minutes of wounding. Secondary qPCR comparison of selected genes showed that oral secretions often increased differential expression relative to mechanical damage alone. The studies provide new insights into early wound responses in chickpea.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.