Organized Disassembly of Photosynthesis During Programmed Cell Death Mediated By Long Chain Bases

Alonso Zavafer,Beatriz King-Díaz,Ariadna González-Solís,Mariana Saucedo-García,Marina Gavilanes-Ruiz,Silvia Palacios-Bahena,Cinthya Tapia De Aquino,Sonia Vázquez-Santana

doi:10.1038/s41598-020-65186-8

Abstract

In plants, pathogen triggered programmed cell death (PCD) is frequently mediated by polar lipid molecules referred as long chain bases (LCBs) or ceramides. PCD interceded by LCBs is a well-organized process where several cell organelles play important roles. In fact, light-dependent reactions in the chloroplast have been proposed as major players during PCD, however, the functional aspects of the chloroplast during PCD are largely unknown. For this reason, we investigated events that lead to disassembly of the chloroplast during PCD mediated by LCBs. To do so, LCB elevation was induced with Pseudomonas syringae pv. tomato (a non-host pathogen) or Fumonisin B1 in Phaseolus vulgaris. Then, we performed biochemical tests to detect PCD triggering events (phytosphingosine rises, MPK activation and H2O2 generation) followed by chloroplast structural and functional tests. Observations of the chloroplast, via optical phenotyping methods combined with microscopy, indicated that the loss of photosynthetic linear electron transport coincides with the organized ultrastructure disassembly. In addition, structural changes occurred in parallel with accumulation of H2O2 inside the chloroplast. These features revealed the collapse of chloroplast integrity and function as a mechanism leading to the irreversible execution of the PCD promoted by LCBs.

Highlights

The simplest plant sphingolipids are long chain bases (LCBs), which have a signaling role during stomata closure, cold response and programmed cell death or PCD[1,2,3,4,5,6,7,8,9]
Evidences dealing with the PCD-Hypersensitive Response (HR) mediated by LCBs suggest an association with the chloroplast: (1) PCD elicited by fumonisin B1 (FB1, a mycotoxin that evokes LCB accumulation25) is light-dependent[16]; (2) PCD induced by FB1 and mediated by MPK611 promotes extensive chloroplast damage and induces H2O2 formation inside the chloroplasts[11,19]
We have shown that two agents inducing PCD by accumulation of LCBs led to the organized decay of the chloroplast function and structure

Summary

Introduction

The simplest plant sphingolipids are long chain bases (LCBs), which have a signaling role during stomata closure, cold response and programmed cell death or PCD (immunity associated)[1,2,3,4,5,6,7,8,9]. A study of the chloroplast and its function during HR-PCD that is mediated by LCBs has not been addressed These and other unknown events dealing with the chloroplast need to be identified and positioned in a single sequence in order to establish a clear functional context. For this reason, we have induced PCD in Phaseulus vulgaris using two LCB eliciting treatments: FB1 and a non-host pathogen that induces HR-PCD.

Methods

Results

Discussion

Conclusion