ABSTRACT
Heterotrimeric G-proteins have been implicated in having a role in many plant signalling pathways. To understand further the role of G-proteins, a preliminary experiment was performed to assess the impact of the G alpha subunit loss-of-function mutation gpa1-1 on the Arabidopsis transcriptome. The analysis indicated that the G alpha subunit may play a role in response to jasmonic acid (JA). Consistent with this, G alpha mutants showed a reduced response to JA in inhibition of chlorophyll accumulation and root growth, whilst G alpha gain-of-function plants overexpressing G alpha showed the opposite phenotype. The levels of JA and related compounds were unaffected in the gpa1-1 mutant, as was autoregulation of the Allene Oxide Synthase (AOS) gene that encodes a key enzyme for JA biosynthesis. In contrast, further analyses using G alpha loss- and gain-of-function Arabidopsis lines indicated that G alpha positively modulates the expression of the Vegetative Storage Protein (VSP) gene. This indicates that the G alpha subunit regulates a subset of JA-regulated genes defining a branch point in this signalling pathway in Arabidopsis. Further analysis of the impact of G alpha loss of function upon the JA-regulated transcriptome using Arabidopsis full genome arrays indicated that up to 29% of genes that are >2-fold regulated by JA in the wild type are misregulated in the G alpha mutant. This supports the observation that a significant proportion of, but not all, JA-regulated gene expression is mediated by G alpha.
Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/metabolism , Cyclopentanes/metabolism , GTP-Binding Protein alpha Subunits/metabolism , Gene Expression Regulation, Plant , Oxylipins/metabolism , Arabidopsis/chemistry , Arabidopsis/genetics , Arabidopsis Proteins/chemistry , Arabidopsis Proteins/genetics , Chlorophyll/metabolism , Endopeptidases/genetics , Endopeptidases/metabolism , GTP-Binding Protein alpha Subunits/chemistry , GTP-Binding Protein alpha Subunits/genetics , Intramolecular Oxidoreductases/genetics , Intramolecular Oxidoreductases/metabolism , Protein MultimerizationABSTRACT
Chloroplasts of photosynthetic organisms harness light energy and convert it into chemical energy. In several land plants, GOLDEN2-LIKE (GLK) transcription factors are required for chloroplast development, as glk1 glk2 double mutants are pale green and deficient in the formation of the photosynthetic apparatus. We show here that glk1 glk2 double mutants of Arabidopsis thaliana accumulate abnormal levels of chlorophyll precursors and that constitutive GLK gene expression leads to increased accumulation of transcripts for antenna proteins and chlorophyll biosynthetic enzymes. To establish the primary targets of GLK gene action, an inducible expression system was used in combination with transcriptome analysis. Following induction, transcript pools were substantially enriched in genes involved in chlorophyll biosynthesis, light harvesting, and electron transport. Chromatin immunoprecipitation experiments confirmed the direct association of GLK1 protein with target gene promoters, revealing a putative regulatory cis-element. We show that GLK proteins influence photosynthetic gene expression independently of the phyB signaling pathway and that the two GLK genes are differentially responsive to plastid retrograde signals. These results suggest that GLK genes help to coregulate and synchronize the expression of a suite of nuclear photosynthetic genes and thus act to optimize photosynthetic capacity in varying environmental and developmental conditions.
Subject(s)
Arabidopsis Proteins/physiology , Arabidopsis/metabolism , Photosynthesis/genetics , Transcription Factors/physiology , Arabidopsis/genetics , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Chlorophyll/biosynthesis , Chlorophyll/genetics , Chlorophyll Binding Proteins , Chromatin Immunoprecipitation , Gene Expression Regulation, Plant , Light-Harvesting Protein Complexes/genetics , Light-Harvesting Protein Complexes/metabolism , Mutation , Phenotype , Photosynthesis/physiology , Phytochrome B/metabolism , Plastids/metabolism , Plastids/physiology , Promoter Regions, Genetic , RNA, Messenger/metabolism , Signal Transduction , Transcription Factors/genetics , Transcription Factors/metabolism , Up-RegulationABSTRACT
Neisseria meningitidis, a causative agent of bacterial meningitis, has a relatively small repertoire of transcription factors, including NMB0573 (annotated AsnC), a member of the Lrp-AsnC family of regulators that are widely expressed in both Bacteria and Archaea. In the present study we show that NMB0573 binds to l-leucine and l-methionine and have solved the structure of the protein with and without bound amino acids. This has shown, for the first time that amino acid binding does not induce significant conformational changes in the structure of an AsnC/Lrp regulator although it does appear to stabilize the octameric assembly of the protein. Transcriptional profiling of wild-type and NMB0573 knock-out strains of N. meningitidis has shown that NMB0573 is associated with an adaptive response to nutrient poor conditions reflected in a reduction in major surface protein expression. On the basis of its structure and the transcriptional response, we propose that NMB0573 is a global regulator in Neisseria controlling responses to nutrient availability through indicators of general amino acid abundance: leucine and methionine.
