Facile Labeling of Sieve Element Phloem-Protein Bodies Using the Reciprocal Oligosaccharide Probe OGA 488.

Pakeeza Azizpor,Lucy Sullivan,Andrew Groover,Aedric Lim

doi:10.3389/fpls.2022.809923

Pakeeza Azizpor, Lucy Sullivan + Show 2 more

Open Access

https://doi.org/10.3389/fpls.2022.809923

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Abstract

Sieve elements of many angiosperms contain structural phloem proteins (P-proteins) that can interact to create large P-protein bodies. P-protein bodies can occlude sieve plates upon injury but the range of functional and physiological roles of P-proteins remains uncertain, in part because of challenges in labeling and visualization methods. Here, we show that a reciprocal oligosaccharide probe, OGA488, can be used in rapid and sensitive labeling of P-protein bodies in Arabidopsis, poplar, snap bean and cucumber in histological sections. OGA488 labeling of knockouts of the two Arabidopsis P-protein-encoding genes, AtSEOR1 and AtSEOR2, indicated that labeling is specific to AtSEOR2. That protein bodies were labeled and visible in Atseor1 knockouts indicates that heterodimerization of AtSEOR1 and AtSEOR2 may not be necessary for P-protein body formation. Double labeling with a previously characterized stain for P-proteins, sulphorhodamine 101, confirmed P-protein labeling and also higher specificity of OGA488 for P-proteins. OGA488 is thus robust and easily used to label P-proteins in histological sections of multiple angiosperm species.

Highlights

Phloem sieve elements are responsible for transport of phloem sap containing photoassimilates, nutrients, signaling molecules, and hormones by bulk flow under pressure (Lucas et al, 2013; Knoblauch et al, 2016)
We found that the OGA488 reciprocal oligosaccharide probe gave reproducible and highly specific staining of P-protein bodies in poplar, Arabidopsis, snap bean and cucumber stems
Using previously characterized loss of function mutants for Arabidopsis P-protein components Arabidopsis thaliana Sieve Element Occlusion-Related 1 (AtSEOR1) and AtSEOR2, we found that AtSEOR2 is responsible for binding OGA488

Summary

Introduction

Phloem sieve elements are responsible for transport of phloem sap containing photoassimilates, nutrients, signaling molecules, and hormones by bulk flow under pressure (Lucas et al, 2013; Knoblauch et al, 2016). This pressurized conduit system is fundamental to plant function and survival, but is susceptible to sap loss upon mechanical injury (Knoblauch and van Bel, 1998). Phloem-protein (P-protein) bodies have long been recognized as conspicuous ultrastructural features within angiosperm sieve elements (Esau and Cronshaw, 1967) These proteinaceous aggregates can take various forms depending on species and developmental stage (Cronshaw, 1981; Evert, 1990). P-protein aggregates can be observed at the sieve plates, suggesting that they play a direct role in occluding sieve plates and reducing phloem

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