Investigating the mechanism of chloroplast singlet oxygen signaling in the Arabidopsis thaliana accelerated cell death 2 mutant

ABSTRACT

As sessile organisms, plants have evolved complex signaling mechanisms to sense stress and acclimate. This includes the use of reactive oxygen species (ROS) generated during dysfunctional photosynthesis to initiate signaling. One such ROS, singlet oxygen (¹O₂), can trigger retrograde signaling, chloroplast degradation, and programmed cell death. However, the signaling mechanisms are largely unknown. Several proteins (e.g. PUB4, OXI1, EX1) are proposed to play signaling roles across three Arabidopsis thaliana mutants that conditionally accumulate chloroplast ¹O₂ (fluorescent in blue light (flu), chlorina 1 (ch1), and plastid ferrochelatase 2 (fc2)). We previously demonstrated that these mutants reveal at least two chloroplast ¹O₂ signaling pathways (represented by flu and fc2/ch1). Here, we test if the ¹O₂-accumulating lesion mimic mutant, accelerated cell death 2 (acd2), also utilizes these pathways. The pub4–6 allele delayed lesion formation in acd2 and restored photosynthetic efficiency and biomass. Conversely, an oxi1 mutation had no measurable effect on these phenotypes. acd2 mutants were not sensitive to excess light (EL) stress, yet pub4–6 and oxi1 both conferred EL tolerance within the acd2 background, suggesting that EL-induced ¹O₂ signaling pathways are independent from spontaneous lesion formation. Thus, ¹O₂ signaling in acd2 may represent a third (partially overlapping) pathway to control cellular degradation.

Keywords:

• Chloroplast
• photosynthesis
• programmed cell death
• reactive oxygen species
• signaling
• singlet oxygen

Acknowledgments

The authors also wish to thank Sophia Daluisio (U of A) for technical assistance with genotyping.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authors’ contributions

MDL and JDW planned and designed the research. MDL performed the assessment of photoinhibition and lesion formation in plants. ANA generated double mutants and confirmed by PCR. JDW conceived the original scope of the project and managed the project. MDL and JDW contributed to data analysis and interpretation, graphical visualization of the data, wrote the manuscript, and reviewed the manuscript. All authors approved the final version.

Data availability statement

All data generated and analyzed during this study are included in this published article.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15592324.2024.2347783

Additional information

Funding

The authors acknowledge the University of Arizona Imaging Cores - Optical Core Facility [RRID:SCR_023355]; the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy grant [DE-SC0019573] awarded to J.D.W and support from the Center for Research on Programmable Plants and the National Science Foundation grant [DBI-2019674]. M.D.L was supported by the [NIH T32 GM136536] training grant and the UA Richard A. Harvill Graduate Fellowship. The funding bodies played no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.