Mesophyll-specific phytochromes impact chlorophyll light-harvesting complexes (LHCs) and non-photochemical quenching

ABSTRACT

Phytochromes regulate light-dependent plastid development and plant growth and development. Prior analyses demonstrated that phytochromes regulate expression of Sigma factor 2 (SIG2), which is involved in plastid transcription and coordinates expression of plastid‐ and nuclear‐encoded genes involved in plastid development, as well as plant growth and development. Mutation of SIG2 impacts distinct aspects of photosynthesis, resulting in elevated levels of cyclic electron flow and nonphotochemical quenching (NPQ). As we initially identified SIG2 expression as misregulated in a line lacking phytochromes in mesophyll tissues (i.e., CAB3::pBVR lines), here we report on an investigation of whether photosynthetic parameters such as NPQ are also disrupted in CAB3::pBVR lines. We determined that a specific parameter of NPQ, i.e., energy-dependent quenching (qE) which is a rapidly induced photoprotective mechanism that dissipates stressful absorption of excess light energy during photosynthesis, is disrupted when mesophyll phytochromes are significantly depleted. The observed reduction in NPQ levels in strong CAB3::pBVR lines is associated with a reduction in the accumulation of Lhcb1 proteins and assembly or stability of light-harvesting complexes (LHCs), especially trimeric LHC. These results implicate mesophyll-localized phytochromes in a specific aspect of phytochrome-mediated NPQ, likely through regulation of chlorophyll synthesis and accumulation and the associated impacts on chlorophyll–protein complexes. This role is distinct from the impact of mesophyll phytochrome-dependent control of SIG2 and associated NPQ regulation.

KEYWORDS:

• Chlorophyll–protein complexes
• light-harvesting complexes (LHC)
• light signaling
• non-photochemical
• quenching
• phytochrome
• photomorphogenesis
• photosynthesis
• stress

Acknowledgments

The authors thank Jeffrey Cruz, Deserah Strand, Ben Lucker, and David M. Kramer for assistance with and discussion of chlorophyll fluorescence measurements and green gel analysis. This research was supported by the Office of Science of the US Department of Energy (grant no. DE‐FG02‐91ER2002 to B.L.M.) and general support to B.L.M. from the National Science Foundation (grant no. MCB‐1515002).

Declaration of Interest

Neither author has financial interests or benefits that have arisen from the direct applications of this research.

Supplementary Materials

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Additional information

Funding

This work was supported by the National Science Foundation [MCB‐1515002]; U.S. Department of Energy [DE‐FG02‐91ER20021].