Table of Contents
IN BRIEF
LARGE-SCALE BIOLOGY ARTICLES
- Tissue- and Cell-Type Specific Transcriptome Profiling of Expanding Tomato Fruit Provides Insights into Metabolic and Regulatory Specialization and Cuticle Formation
This study uses laser capture microdissection coupled with pyrosequencing to characterize the cell- and tissue-type transcriptomes of the pericarp of expanding tomato fruits. This provides new insights into the spatial distribution of expression of structural and regulatory genes associated with many metabolic pathways, and a cuticle lining the inner pericarp surface is described.
- Plastid Proteome Assembly without Toc159: Photosynthetic Protein Import and Accumulation of N-Acetylated Plastid Precursor Proteins
Proteome analysis and genome-wide transcript profiling in mutant lines deficient in Toc159 define putative Toc159-independent and Toc159-dependent precursor proteins and provide insight into Toc159 receptor function and regulation of plastid protein import.
RESEARCH ARTICLES
- Regulation of Compound Leaf Development in Medicago truncatula by Fused Compound Leaf1, a Class M KNOX Gene
This study describes isolation and characterization of loss-of-function mutants of Fused Compound Leaf1 (FCL1) in Medicago truncatula that encodes a class M KNOX transcription factor. Phenotypic and genetic studies demonstrate that FCL1 is required for boundary separation of leaflet primordia and elongation of petioles. Models of genetic interactions of fcl1 with sgl1 and palm1 are discussed.
- A Small-Molecule Screen Identifies l-Kynurenine as a Competitive Inhibitor of TAA1/TAR Activity in Ethylene-Directed Auxin Biosynthesis and Root Growth in Arabidopsis
In this work, Kyn is identified as an auxin biosynthesis inhibitor that effectively and selectively targets TAA1-like Trp aminotransferases. Moreover, it describes a previously undiscovered positive feedback loop between auxin biosynthesis and ethylene signaling pathways in roots.
- The Arabidopsis YUCCA1 Flavin Monooxygenase Functions in the Indole-3-Pyruvic Acid Branch of Auxin Biosynthesis
The flavin monooxygenase YUC1 and the Trp aminotransferase TAA1 were previously believed to function in two independent auxin biosynthetic pathways. The genetic and biochemical evidence presented herein demonstrates that the YUC1 and TAA1 gene families work in a single route, providing a new simplified view of how auxin is produced in plants.
- Functional Profiling Identifies Genes Involved in Organ-Specific Branches of the PIF3 Regulatory Network in Arabidopsis
This work identifies genes that are regulated by PIF3 in the dark using a microarray-based approach and profiles the function of 13 of these genes during skotomorphogenesis. Four are novel regulators of seedling deetiolation, and each regulates a specific facet of seedling etiolation, indicating that there is branching in the signaling pathway downstream of PIF3.
- Evidence for a SAL1-PAP Chloroplast Retrograde Pathway That Functions in Drought and High Light Signaling in Arabidopsis
This work describes a chloroplast-to-nucleus retrograde signaling pathway involving SAL1, a chloroplast and mitochondrial enzyme that degrades the phosphonucleotide 3′-phosphoadenosine 5′-phosphate (PAP). In the absence of SAL1 or in response to drought and high light, PAP accumulates and can move between the chloroplast and the nucleus, where it inhibits exoribonucleases, thereby inducing stress-responsive genes.
- Arabidopsis α Aurora Kinases Function in Formative Cell Division Plane Orientation
This work reports on a genetic approach to unravel the developmental function of the group α Aurora kinases by analyzing a viable double mutant. The results show that α Aurora kinases are functionally divergent from the β Aurora kinase and suggest that α Aurora kinases regulate formative division plane orientation throughout development.
- AXY8 Encodes an α-Fucosidase, Underscoring the Importance of Apoplastic Metabolism on the Fine Structure of Arabidopsis Cell Wall Polysaccharides
Characterization of an Arabidopsis thaliana mutant with an altered structure of the cell wall hemicellulose xyloglucan lead to the identification of an apoplastic fucosidase, AXY8. The data suggest that apoplastic trimming of cell wall polysaccharides by plant glycosylhydrolases plays a major role in generating the structural heterogeneity and complexity found in wall polysaccharides.
- O-Acetylation of Arabidopsis Hemicellulose Xyloglucan Requires AXY4 or AXY4L, Proteins with a TBL and DUF231 Domain
Most plant cell wall polysaccharides are O-acetylated. However, the acetyltransferases were elusive. Using a forward genetic approach, a putative xyloglucan O-acetyltransferase has now been identified in an unexpected gene family. This opens up future research into the identification of other O-acetyltransferases and the elucidation of the molecular mechanism of polysaccharide O-acetylation.
- Euchromatic Subdomains in Rice Centromeres Are Associated with Genes and Transcription
This work examines the distribution of four euchromatic histone modification marks (H3K4me2, H3K4me3, H3K36me3, and H3K4K9ac) within rice centromeres and finds that these marks are almost exclusively associated with centromeric subdomains that contain actively transcribed genes.
- Transcriptional Regulation of Arabidopsis LEAFY COTYLEDON2 Involves RLE, a cis-Element That Regulates Trimethylation of Histone H3 at Lysine-27
The authors conducted genetic, molecular, and functional analyses of the promoter region that controls the expression of LEC2, a key seed regulatory gene. They characterized three cis-elements, including RLE, which is necessary for histone H3 trimethylation. The results provide data about the transcriptional regulatory network that controls seed development and chromatin regulation of plant gene expression.
- Transcriptomic Analysis Reveals Calcium Regulation of Specific Promoter Motifs in Arabidopsis
Many stimuli cause brief elevations in the concentration of calcium in plant cells, and these changes trigger appropriate responses from the cell. This work shows that specific short DNA sequences in some plant genes recognize such changes in calcium levels and allow these genes to be activated; this information aids our understanding of how plants respond to specific environmental stresses.
- The Phosphoglucan Phosphatase Like Sex Four2 Dephosphorylates Starch at the C3-Position in Arabidopsis
This work identifies an enzyme, named Like Sex Four2 (LSF2), that hydrolyzes the phosphate group from the C3-position of glucosyl residues of starch. The lsf2 mutation in Arabidopsis thaliana leads to modified starch with elevated levels of C3-bound phosphate.
- Triterpene Functional Genomics in Licorice for Identification of CYP72A154 Involved in the Biosynthesis of Glycyrrhizin
This work reports the identification of a cytochrome P450 monooxygenase that is responsible for the biosynthesis of glycyrrhizin, a triterpenoid saponin found in licorice. The results reveal a function of CYP72A subfamily proteins as triterpene-oxidizing enzymes and provide proof of concept for engineering the production of high-value triterpenoid products in yeasts.
- The Arabidopsis Glucosyltransferase UGT76B1 Conjugates Isoleucic Acid and Modulates Plant Defense and Senescence
The orphan small-molecule glycosyltransferase UGT76B1 is a novel player in plant pathogen defense that represses the salicylic acid pathway, yet enhances the jasmonic acid pathway. A nontargeted metabolome approach led to the identification of its substrate, 2-hydroxy-3-methyl-pentanoic acid, which itself was able to induce resistance against Pseudomonas syringae infection.
- Programmed Cell Death Occurs Asymmetrically during Abscission in Tomato
This work examines abscission in tomato and finds that it is associated with programmed cell death and expression of the RNase LX, both of which occur on the distal side of the abscission zone, indicating asymmetric processes occurring during abscission.
COMMENTARY