Rational Design of an Auxin Antagonist of the SCF TIR1 Auxin Receptor Complex

The vacuole is the most prominent compartment in plant cells and is important for ion and protein storage. In our effort to search for key regulators in the plant vacuole sorting pathway, ribosomal large subunit 4 (rpl4d) was identified as a translational mutant defective in both vacuole trafficking and normal development. Polysome profiling of the rpl4d mutant showed reduction in polysome-bound mRNA compared with wild-type, but no significant change in the general mRNA distribution pattern. Ribsomal profiling data indicated that genes in the lipid metabolism pathways were translationally down-regulated in the rpl4d mutant. Live imaging studies by Nile red staining suggested that both polar and nonpolar lipid accumulation was reduced in meristem tissues of rpl4d mutants. Pharmacological evidence showed that sterol and sphingolipid biosynthetic inhibitors can phenocopy the defects of the rpl4d mutant, including an altered vacuole trafficking pattern. Genetic evidence from lipid biosynthetic mutants indicates that alteration in the metabolism of either sterol or sphingolipid biosynthesis resulted in vacuole trafficking defects, similar to the rpl4d mutant. Tissue-specific complementation with key enzymes from lipid biosynthesis pathways can partially rescue both vacuole trafficking and auxin-related developmental defects in the rpl4d mutant. These results indicate that lipid metabolism modulates auxin-mediated tissue differentiation and endomembrane trafficking pathways downstream of ribosomal protein function.

“…3 E and G). A similar secretion phenotype could be detected when treated with auxin signal transduction inhibitor auxinole (54) for the same time period (Fig. 3 F and G).…”

Section: Lipid Biosynthesis Inhibitors Induced Vacuole Trafficking Desupporting

confidence: 78%

Arabidopsis ribosomal proteins control vacuole trafficking and developmental programs through the regulation of lipid metabolism

Sun

Hicks

et al. 2014

“…4D). Moreover, treatment of seedlings with auxinole, a specific inhibitor of the nuclear auxin receptors, and thus auxin response (22,23), abolished this division when applied at mild concentration (Fig. 4 E and F), suggesting it is particularly sensitive to changes in auxin activity.…”

Section: Resultsmentioning

confidence: 93%

Molecular genetic framework for protophloem formation

Rodríguez-Villalón

Gujas

Kang

et al. 2014

173

286

The phloem performs essential systemic functions in tracheophytes, yet little is known about its molecular genetic specification. Here we show that application of the peptide ligand CLAVATA3/EMBRYO SURROUNDING REGION 45 (CLE45) specifically inhibits specification of protophloem in Arabidopsis roots by locking the sieve element precursor cell in its preceding developmental state. CLE45 treatment, as well as viable transgenic expression of a weak CLE45 G6T variant, interferes not only with commitment to sieve element fate but also with the formative sieve element precursor cell division that creates protophloem and metaphloem cell files. However, the absence of this division appears to be a secondary effect of discontinuous sieve element files and subsequent systemically reduced auxin signaling in the root meristem. In the absence of the formative sieve element precursor cell division, metaphloem identity is seemingly adopted by the normally procambial cell file instead, pointing to possibly independent positional cues for metaphloem formation. The protophloem formation and differentiation defects in brevis radix (brx) and octopus (ops) mutants are similar to those observed in transgenic seedlings with increased CLE45 activity and can be rescued by loss of function of a putative CLE45 receptor, BARELY ANY MERI-STEM 3 (BAM3). Conversely, a dominant gain-of-function ops allele or mild OPS dosage increase suppresses brx defects and confers CLE45 resistance. Thus, our data suggest that delicate quantitative interplay between the opposing activities of BAM3-mediated CLE45 signals and OPS-dependent signals determines cellular commitment to protophloem sieve element fate, with OPS acting as a positive, quantitative master regulator of phloem fate. stem cell | division plane switching

“…1 A-C). This increase was sensitive to auxinole (13), a designated inhibitor of Transport Inhibitor Response 1 (TIR1)/Auxin Signaling F-Box (AFB) auxin receptors ( Fig. S1 G-L).To define further the actin filament organization beyond the cell cortex, we used gated stimulated emission depletion (gSTED) superresolution live-cell imaging and performed defined z-stack imaging on epidermal root cells.…”

Section: Resultsmentioning

confidence: 99%

Actin-dependent vacuolar occupancy of the cell determines auxin-induced growth repression

Scheuring

Löfke

Krüger

et al. 2015

134

151

The cytoskeleton is an early attribute of cellular life, and its main components are composed of conserved proteins. The actin cytoskeleton has a direct impact on the control of cell size in animal cells, but its mechanistic contribution to cellular growth in plants remains largely elusive. Here, we reveal a role of actin in regulating cell size in plants. The actin cytoskeleton shows proximity to vacuoles, and the phytohormone auxin not only controls the organization of actin filaments but also impacts vacuolar morphogenesis in an actindependent manner. Pharmacological and genetic interference with the actin-myosin system abolishes the effect of auxin on vacuoles and thus disrupts its negative influence on cellular growth. SEMbased 3D nanometer-resolution imaging of the vacuoles revealed that auxin controls the constriction and luminal size of the vacuole. We show that this actin-dependent mechanism controls the relative vacuolar occupancy of the cell, thus suggesting an unanticipated mechanism for cytosol homeostasis during cellular growth.auxin | vacuole | actin cytoskeleton | cell growth