David McCurdy

Asymmetric wall ingrowth deposition in Arabidopsis phloem parenchyma transfer cells is tightly associated with sieve elements

Publisher: Cold Spring Harbor Laboratory

Date: 05-01-2022

DOI: 10.1101/2022.01.04.475004

Abstract: In Arabidopsis, polarized deposition of wall ingrowths in phloem parenchyma (PP) transfer cells (TCs) occurs adjacent to cells of the sieve element/companion cell (SE/CC) complex. However, the spatial relationships between these different cell types in minor veins, where phloem loading occurs, are poorly understood. PP TC development and wall ingrowth localization were compared to other phloem cells in leaves of Col-0 and the transgenic lines AtSUC2::AtSTP9-GFP and AtSWEET11::AtSWEET11-GFP that identify CCs and PP respectively. The development of PP TCs in minor veins, indicated by deposition of wall ingrowths, proceeded basipetally in leaves. However, not all PP develop ingrowths and higher levels of wall ingrowth deposition occur in abaxial-compared to adaxial-positioned PP TCs. Furthermore, the deposition of wall ingrowths was exclusively initiated on and preferentially covered the PP TC/SE interface, rather than the PP TC/CC interface, and only occurred in PP cells that were adjacent to SEs. Collectively, these results demonstrate the dominant impact of SEs on wall ingrowth deposition in PP TCs and suggest the existence of two sub-types of PP cells in leaf minor veins. Compared to PP cells, PP TCs showed more abundant accumulation of AtSWEET11-GFP, indicating functional differences in phloem loading between PP and PP TCs. Wall ingrowth deposition in phloem parenchyma transfer cells of Arabidopsis leaf minor veins is initiated adjacent to sieve elements, rather than companion cells, and expands to preferentially cover this interface.

Wall ingrowth deposition in phloem parenchyma transfer cells in Arabidopsis: Heteroblastic variations and a potential role in pathogen defence

Publisher: Informa UK Limited

Date: 03-06-2017

DOI: 10.1080/15592324.2017.1338226

Asymmetric wall ingrowth deposition in Arabidopsis phloem parenchyma transfer cells is tightly associated with sieve elements

Publisher: Oxford University Press (OUP)

Date: 24-05-2022

DOI: 10.1093/JXB/ERAC234

Abstract: In Arabidopsis, polarized deposition of wall ingrowths in phloem parenchyma (PP) transfer cells (TCs) occurs adjacent to cells of the sieve element/companion cell (SE/CC) complex. However, the spatial relationships between these different cell types in minor veins, where phloem loading occurs, are poorly understood. PP TC development and wall ingrowth localization were compared with those of other phloem cells in leaves of Col-0 and the transgenic lines AtSUC2::AtSTP9-GFP (green fluorescent protein) and AtSWEET11::AtSWEET11-GFP that identify CCs and PP cells, respectively. The development of PP TCs in minor veins, indicated by deposition of wall ingrowths, proceeded basipetally in leaves. However, not all PP cells develop wall ingrowths, and higher levels of deposition occur in abaxial- compared with adaxial-positioned PP TCs. Furthermore, the deposition of wall ingrowths was exclusively initiated on and preferentially covered the PP TC/SE interface, rather than the PP TC/CC interface, and only occurred in PP cells that were adjacent to SEs. Collectively, these results demonstrate a tight association between SEs and wall ingrowth deposition in PP TCs and suggest the existence of two subtypes of PP cells in leaf minor veins. Compared with PP cells, PP TCs showed more abundant accumulation of AtSWEET11–GFP, indicating functional differences in phloem loading between PP and PP TCs.

The Orchid Velamen: A Model System for Studying Patterned Secondary Cell Wall Development?

Publisher: MDPI AG

Date: 02-07-2021

DOI: 10.3390/PLANTS10071358

Abstract: Understanding the mechanisms through which plants generate secondary cell walls is of more than academic interest: the physical properties of plant-derived materials, including timber and textiles, all depend upon secondary wall cellulose organization. Processes controlling cellulose in the secondary cell wall and their reliance on microtubules have been documented in recent decades, but this understanding is complicated, as secondary walls normally form in the plant’s interior where live cell imaging is more difficult. We investigated secondary wall formation in the orchid velamen, a multicellular epidermal layer found around orchid roots that consists of dead cells with lignified secondary cell walls. The patterns of cell wall ridges that form within the velamen vary between different orchid species, but immunolabelling demonstrated that wall deposition is controlled by microtubules. As these patterning events occur at the outer surface of the root, and as orchids are adaptable for tissue culture and genetic manipulation, we conclude that the orchid root velamen may indeed be a suitable model system for studying the organization of the plant cell wall. Notably, roots of the commonly grown orchid Laelia anceps appear ideally suited for developing this research.

ACTIN7 Is Required for Perinuclear Clustering of Chloroplasts during Arabidopsis Protoplast Culture

Publisher: MDPI AG

Date: 10-02-2020

DOI: 10.3390/PLANTS9020225

Abstract: In Arabidopsis, the actin gene family comprises eight expressed and two non-expressed ACTIN (ACT) genes. Of the eight expressed isoforms, ACT2, ACT7, and ACT8 are differentially expressed in vegetative tissues and may perform specific roles in development. Using tobacco mesophyll protoplasts, we previously demonstrated that actin-dependent clustering of chloroplasts around the nucleus prior to cell ision ensures unbiased chloroplast inheritance. Here, we report that actin-dependent chloroplast clustering in Arabidopsis mesophyll protoplasts is defective in act7 mutants, but not act2-1 or act8-2. ACT7 expression was upregulated during protoplast culture whereas ACT2 and ACT8 expression did not substantially change. In act2-1, ACT7 expression increased in response to loss of ACT2, whereas in act7-1, neither ACT2 nor ACT8 expression changed appreciably in response to the absence of ACT7. Semi-quantitative immunoblotting revealed increased actin concentrations during culture, although total actin in act7-1 was only two-thirds that of wild-type or act2-1 after 96 h culture. Over-expression of ACT2 and ACT8 under control of ACT7 regulatory sequences restored normal levels of chloroplast clustering. These results are consistent with a requirement for ACT7 in actin-dependent chloroplast clustering due to reduced levels of actin protein and gene induction in act7 mutants, rather than strong functional specialization of the ACT7 isoform.

Sucrose regulates wall ingrowth deposition in phloem parenchyma transfer cells in Arabidopsis via affecting phloem loading activity

Publisher: Oxford University Press (OUP)

Date: 20-05-2020

DOI: 10.1093/JXB/ERAA246

Abstract: In Arabidopsis thaliana, phloem parenchyma transfer cells (PPTCs) occur in leaf minor veins and play a pivotal role in phloem loading. Wall ingrowth formation in PPTCs is induced by the phloem loading activity of these cells, which is regulated by sucrose (Suc). The effects of endogenous versus exogenous Suc on wall ingrowth deposition, however, differ. Elevating endogenous Suc levels by increased light enhanced wall ingrowth formation, whereas lowering endogenous Suc levels by dark treatment or genetically in ch-1 resulted in lower levels of deposition. In contrast, exogenously applied Suc, or Suc derived from other organs, repressed wall ingrowth deposition. Analysis of pAtSUC2::GFP plants, used as a marker for phloem loading status, suggested that wall ingrowth formation is correlated with phloem loading activity. Gene expression analysis revealed that exogenous Suc down-regulated expression of AtSWEET11 and 12, whereas endogenous Suc up-regulated AtSWEET11 expression. Analysis of a TREHALOSE 6-PHOSPHATE (T6P) SYNTHASE overexpression line and the hexokinase (HXK)-null mutant, gin2-1, suggested that Suc signalling of wall ingrowth formation is independent of T6P and HXK. Collectively, these results are consistent with the conclusion that Suc regulates wall ingrowth formation via affecting Suc exporting activity in PPTCs.

Phi thickenings in Brassica oleracea roots are induced by osmotic stress and mechanical effects, both involving jasmonic acid

Publisher: Oxford University Press (OUP)

Date: 22-10-2021

DOI: 10.1093/JXB/ERAB468

Abstract: Phi thickenings are peculiar secondary cell wall thickenings found in radial walls of cortical cells in plant roots. However, while thickenings are widespread in the plant kingdom, research into their development has been lacking. Here, we describe a simple system for rapid induction of phi thickenings in primary roots of Brassica. Four-day-old seedlings were transferred from control agar plates to new plates containing increased levels of osmotica. Phi thickening development occurred within a narrow region of the differentiation zone proportional to osmolarity, with cellulose deposition and lignification starting after 12h and 15h, respectively. However, osmoprotectants not only failed to induce phi thickenings, but inhibited induction when tested in combination with thickening-inducing osmotica. An independent, biomechanical pathway exists regulating phi thickening induction, with root growth rates and substrate texture being important factors in determining thickening induction. Phi thickening development is also controlled by stress-related plant hormones, most notably jasmonic acid, but also abscisic acid. Our research not only provides the first understanding of the developmental pathways controlling phi thickening induction, but also provides tools with which the functions of these enigmatic structures might be clarified.

Phi thickenings in roots: novel secondary wall structures responsive to biotic and abiotic stresses

Publisher: Oxford University Press (OUP)

Date: 18-05-2019

DOI: 10.1093/JXB/ERZ240

Abstract: Phi thickenings are specialized secondary walls found in root cortical cells. Despite their widespread occurrence throughout the plant kingdom, these specialized thickenings remain poorly understood. First identified by Van Tieghem in 1871, phi thickenings are a lignified and thickened cell wall band that is deposited inside the primary wall, as a ring around the cells’ radial walls. Phi thickenings can, however, display structural variations including a fine, reticulate network of wall thickenings extending laterally from the central lignified band. While phi thickenings have been proposed to mechanically strengthen roots, act as a permeability barrier to modulate solute movement, and regulate fungal interactions, these possibilities remain to be experimentally confirmed. Furthermore, since temporal and spatial development of phi thickenings varies widely between species, thickenings may perform erse roles in different species. Phi thickenings can be induced by abiotic stresses in different species they can, for ex le, be induced by heavy metals in the Zn/Cd hyperaccumulator Thlaspi caerulescens, and in a cultivar-specific manner by water stress in Brassica. This latter observation provides an experimental platform to probe phi thickening function, and to identify genetic pathways responsible for their formation. These pathways might be expected to differ from those involved in secondary wall formation in xylem, since phi thickening deposition in not linked to programmed cell death.

Heteroblastic Development of Transfer Cells Is Controlled by the microRNA miR156/SPL Module

Publisher: Oxford University Press (OUP)

Date: 12-01-2017

DOI: 10.1104/PP.16.01741

The University Of Newcastle

Location: Australia

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Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0989861

Start Date: 2009

End Date: 12-2010

Amount: $650,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0556217

Start Date: 2005

End Date: 12-2007

Amount: $300,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0211014

Start Date: 2001

End Date: 12-2002

Amount: $337,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE100100008

Start Date: 2010

End Date: 12-2010

Amount: $350,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0989084

Start Date: 2009

End Date: 12-2009

Amount: $275,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0561173

Start Date: 2005

End Date: 12-2005

Amount: $207,189.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP110100770

Start Date: 01-2011

End Date: 12-2017

Amount: $294,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE140100133

Start Date: 2014

End Date: 12-2014

Amount: $230,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0452977

Start Date: 07-2004

End Date: 12-2005

Amount: $329,504.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0664626

Start Date: 2006

End Date: 12-2011

Amount: $322,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE110100130

Start Date: 2011

End Date: 11-2013

Amount: $500,000.00

Funder: Australian Research Council