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Most molecular processes during plant development occur with a particular spatio-temporal specificity. Thus far, it has remained technically challenging to capture dynamic protein-protein interactions within a growing organ, where the interplay between cell division and cell expansion is instrumental. Here, we combined high-resolution sampling of the growing maize (Zea mays) leaf with tandem affinity purification followed by mass spectrometry. Our results indicate that the growth-regulating SWI/SNF chromatin remodeling complex associated with ANGUSTIFOLIA3 (AN3) was conserved within growing organs and between dicots and monocots. Moreover, we were able to demonstrate the dynamics of the AN3-interacting proteins within the growing leaf, since copurified GROWTH-REGULATING FACTORs (GRFs) varied throughout the growing leaf. Indeed, GRF1, GRF6, GRF7, GRF12, GRF15, and GRF17 were significantly enriched in the division zone of the growing leaf, while GRF4 and GRF10 levels were comparable between division zone and expansion zone in the growing leaf. These dynamics were also reflected at the mRNA and protein levels, indicating tight developmental regulation of the AN3-associated chromatin remodeling complex. In addition, the phenotypes of maize plants overexpressing miRNA396a-resistant GRF1 support a model proposing that distinct associations of the chromatin remodeling complex with specific GRFs tightly regulate the transition between cell division and cell expansion. Together, our data demonstrate that advancing from static to dynamic protein-protein interaction analysis in a growing organ adds insights in how developmental switches are regulated. [ABSTRACT FROM AUTHOR]

Post-transcriptional modifications on transfer RNA (tRNA) molecules occur frequently but their implication on the translational regulation is only recently becoming fully appreciated. Several tRNA molecules in the eukaryotic cytoplasm carry a methoxycarbonylmethyl (mcm) or carbamoylmethyl (ncm) group on their wobble uridine to ensure the efficient and reliable decoding of A- or G-ending codons. Evidence suggests that the six subunits of the conserved Elongator complex are all required for an early step in the synthesis of the mcm and ncm groups in Saccharomyces cerevisiae as well as in Caenorhabditis elegans. In this issue of Molecular Microbiology, Mehlgarten et al. convincingly show that the tRNA-modifying role of Elongator is also conserved in the plant Arabidopsis thaliana. Moreover, combinations of subunits of the Arabidopsis Elongator complex can structurally and functionally complement deletion mutants in yeast and substitute for the tRNA modification activity. The data suggest that Elongator might be a unique multitasking complex with at least two conserved roles in all eukaryotes, i.e. transcriptional activation via histone acetylation in the nucleus and translational control through tRNA modification in the cytoplasm. [ABSTRACT FROM AUTHOR]

In eukaryotes, transcription of protein-encoding genes is strongly regulated by posttranslational modifications of histones that affect the accessibility of the DNA by RNA polymerase II (RNAPII). The Elongator complex was originally identified in yeast as a histone acetyltransferase (HAT) complex that activates RNAPII-mediated transcription. In Arabidopsis thaliana, the Elongator mutants elo1, elo2, and elo3 with decreased leaf and primary root growth due to reduced cell proliferation identified homologs of components of the yeast Elongator complex, E1p4, Elp1, and E1p3, respectively. Here we show that the Elongator complex was purified from plant cell cultures as a six-component complex. The role of plant Elongator in transcription elongation was supported by colocalization of the HAT enzyme, ELO3, with euchromatin and the phosphorylated form of RNAPII, and reduced histone H3 lysine 14 acetylation at the coding region of the SHORTHYPOCOTYL 2 auxin repressor and the LAX2 auxin influx carrier gene with reduced expression levels in the eIo3 mutant. Additional auxin-related genes were down-regulated in the transcriptome of elo mutants but not targeted by the Elongator HAT activity showing specificity in target gene selection. Biological relevance was apparent by auxin-related phenotypes and marker gene analysis. Ethylene and jasmonic acid signaling and abiotic stress responses were up-regulated in the elo transcriptorne and might contribute to the pleiotropic elo phenotype. Thus, although the structure of Elongator and its substrate are conserved, target gene selection has diverged, showing that auxin signaling and influx are under chromatin control. [ABSTRACT FROM AUTHOR]