SABRE populates ER domains essential for cell plate maturation and cell expansion influencing cell and tissue patterning.

Xiaohang Cheng,Magdalena Bezanilla

doi:10.7554/elife.65166

Abstract

SABRE, which is found throughout eukaryotes and was originally identified in plants, mediates cell expansion, division plane orientation, and planar polarity in plants. How and where SABRE mediates these processes remain open questions. We deleted SABRE in Physcomitrium patens, an excellent model for cell biology. SABRE null mutants were stunted, similar to phenotypes in seed plants. Additionally, polarized growing cells were delayed in cytokinesis, sometimes resulting in catastrophic failures. A functional SABRE fluorescent fusion protein localized to dynamic puncta on regions of the endoplasmic reticulum (ER) during interphase and at the cell plate during cell division. Without SABRE, cells accumulated ER aggregates and the ER abnormally buckled along the developing cell plate. Notably, callose deposition was delayed in ∆sabre, and in cells that failed to divide, abnormal callose accumulations formed at the cell plate. Our findings revealed a surprising and fundamental role for the ER in cell plate maturation.

Highlights

Due to their sessile nature, plants cannot run away from environmental stimuli and instead must adjust to their environment by regulating growth patterns
We found that Dsabre plants are stunted, exhibiting defects in polarized growth, diffuse cell expansion, and dramatic cell division failures accompanied by deposition of brown material into the cytoplasm often resulting in cell death
Consistent with the finding that microtubules were not affected in Dsabre plants (Figure 2—figure supplement 1A, C) and that SABRE localizes to the nascent cell plate even in late phragmoplasts that lack microtubules (Figure 4B), we found that cortical SABRE puncta did not associate with microtubules (Figure 4C, Figure 4, Video 6)

Summary

Introduction

Due to their sessile nature, plants cannot run away from environmental stimuli and instead must adjust to their environment by regulating growth patterns. Asymmetric cell divisions define the stomatal guard cells (Dong et al, 2009), and restricted expansion in cells defines the jigsawshaped epidermal cells (Sapala et al, 2019) In filamentous cells such as pollen tubes and root hairs in seed plants, polarized secretion of flexible wall material to the cell apex leads to cell expansion occurring only at the apex of the cell (Bascom et al, 2018; Chen et al, 2018; Dehors et al, 2019; Orr et al, 2020). Transcription factors that initiate root hair cell fate were altered, resulting in the formation of root hairs from ectopic sites These studies have pointed to a critical role for SABRE in regulating plant polarity at both cell and tissue levels (Pietra et al, 2015). These results indicate that SABRE regulates plant cell expansion and division via its interaction with the ER, pointing to a fundamentally important role for the ER in plant cell and tissue morphogenesis

Results

Discussion

Materials and methods

Funding Funder National Science Foundation