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Review
. 2020 May 9;71(9):2505-2512.
doi: 10.1093/jxb/erz567.

Diverse regulation of plasmodesmal architecture facilitates adaptation to phloem translocation

Dawei Yan  1 , Yao Liu  1
Affiliations
Review

Diverse regulation of plasmodesmal architecture facilitates adaptation to phloem translocation

Dawei Yan et al. J Exp Bot. .

Abstract

The long-distance translocation of nutrients and mobile molecules between different terminals is necessary for plant growth and development. Plasmodesmata-mediated symplastic trafficking plays an important role in accomplishing this task. To facilitate intercellular transport, plants have evolved diverse plasmodesmata with distinct internal architecture at different cell-cell interfaces along the trafficking route. Correspondingly, different underlying mechanisms for regulating plasmodesmal structures have been gradually revealed. In this review, we highlight recent studies on various plasmodesmal architectures, as well as relevant regulators of their de novo formation and transition, responsible for phloem loading, transport, and unloading specifically. We also discuss the interesting but unaddressed questions relating to, and potential studies on, the adaptation of functional plasmodesmal structures.

Keywords: Callose; phloem translocation; plasmodesmata; symplastic trafficking; unloading.

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Figures

Fig. 1.
Fig. 1.
A schematic diagram showing the major localized plasmodesmal components that are involved in permeability control. These components are localized at the plasmodesma (left panel, except choline) and modulate plasmodesmal permeability by different mechanisms (right panel). Remorin, sterol, PDLPs, and PDCBs can induce callose biosynthesis and thus restrict plasmodesmal aperture. Remorin, MCTPs and sphingolipids affect the ER–plasma membrane connection and control the cytoplasmic sleeve space. Myosin and actin were previously reported, without a detailed working model, to alter the plasmodesmal permeability. DT, desmotubule; ER, endoplasmic reticulum; MCTP, multiple C2 domains and transmembrane region protein; PDCB, PD CALLOSE-BINDING PROTEIN; PDLP, PD-LOCALIZED PROTEIN; PM, plasma membrane.
Fig. 2.
Fig. 2.
Diverse plasmodesmal forms and regulators responsible for phloem translocation. In source tissues, mobile molecules that are present in CCs diffuse through PPUs into SEs, followed by long-distance transport in SE cells that are connected by sieve pores within sieve plates. At the region of differentiated PSE, those molecules are batch-unloaded into PPP via funnel-shaped PD, and subsequently moved further into the endodermis. The post-SE unloading process through the PPP–endodermis interface can be modulated by the dynamic proportion of type I and type II PD. The key genes that play regulatory roles are listed. CC, companion cell; En, endodermis; ER, endoplasmic reticulum; PPP, phloem pole pericycle; PPU, pore-PD unit; SE, sieve element.
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