title: Heteroblastic Development of Transfer Cells Is Controlled by the microRNA miR156/SPL Module.
abstract: We report that wall ingrowth deposition in phloem parenchyma (PP) transfer cells (TCs) in leaf veins of Arabidopsis (Arabidopsis thaliana) represents a novel trait of heteroblasty. Development of PP TCs involves extensive deposition of wall ingrowths adjacent to cells of the sieve element/companion cell complex. These PP TCs potentially facilitate phloem loading by enhancing efflux of symplasmic Suc for subsequent active uptake into cells of the sieve element/companion cell complex. PP TCs with extensive wall ingrowths are ubiquitous in mature cotyledons and juvenile leaves, but dramatically less so in mature adult leaves, an observation consistent with PP TC development reflecting vegetative phase change (VPC) in Arabidopsis. Consistent with this conclusion, the abundance of PP TCs with extensive wall ingrowths varied across rosette development in three ecotypes displaying differing durations of juvenile phase, and extensive deposition of wall ingrowths was observed in rejuvenated leaves following prolonged defoliation. PP TC development across juvenile, transition, and adult leaves correlated positively with levels of miR156, a major regulator of VPC in plants, and corresponding changes in wall ingrowth deposition were observed when miR156 was overexpressed or its activity suppressed by target mimicry. Analysis of plants carrying miR156-resistant forms ofSQUAMOSA PROMOTER BINDING PROTEIN LIKE(SPL) genes showed that wall ingrowth deposition was increased inSPL9-group but notSPL3-group genes, indicating thatSPL9-group genes may function as negative regulators of wall ingrowth deposition in PP TCs. Collectively, our results point to wall ingrowth deposition in PP TCs being under control of the genetic program regulating VPC.
authors.affiliation: Centre for Plant Science, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
authors.forename: Suong T T
authors.identifier: 0000-0002-4997-9649
authors.initials: ST
authors.lastname: Nguyen
authors.affiliation: Centre for Plant Science, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
authors.forename: Teighan
authors.initials: T
authors.lastname: Greaves
authors.affiliation: Centre for Plant Science, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia david.mccurdy@newcastle.edu.au.
authors.forename: David W
authors.identifier: 0000-0003-2083-7783
authors.initials: DW
authors.lastname: McCurdy
mesh_terms: D017360:Arabidopsis / Q000033:anatomy & histology / Q000166:cytology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D035683:MicroRNAs / Q000235:genetics*; D018613:Microscopy, Confocal; D009154:Mutation; D010641:Phenotype; D052585:Phloem / Q000033:anatomy & histology / Q000166:cytology / Q000235:genetics*; D018515:Plant Leaves / Q000033:anatomy & histology / Q000166:cytology / Q000235:genetics*; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000235:genetics*
chemical_list: D029681:Arabidopsis Proteins; D035683:MicroRNAs; C559759:Mirn156 microRNA, Arabidopsis; C531404:SPL9 protein, Arabidopsis; D015534:Trans-Activators