Chilling- and dark-regulated photoprotection in Miscanthus, an economically important C4 grass.

Tolerance of chilling dictates the geographical distribution, establishment, and productivity of C₄ crops. Chilling reduces enzyme rate, limiting the sink for the absorbed light energy leading to the need for quick energy dissipation via non-photochemical quenching (NPQ). Here, we characterize NPQ upon chilling in three Miscanthus accessions representing diverse chilling tolerance in C₄ grasses. High chilling tolerant accessions accumulate substantial amounts of zeaxanthin during chilling nights in both field and growth chamber settings. Chilling-induced zeaxanthin accumulation in the dark enhances rate of NPQ induction by 66% in the following morning. Based on our data, the emerging ways for the unique regulation of NPQ include post-translational regulation of violaxanthin de-epoxidase (VDE), VDE cofactor accessibility, and absence of transcriptional upregulation of zeaxanthin conversion back to violaxanthin. In the future, more studies will be required to obtain further evidence for these ways contributions to the chilling-dark regulation of NPQ. Engineering dark accumulation of zeaxanthin will help improve crop chilling tolerance and promote sustainable production by allowing early spring planting to maximize the use of early-season soil moisture. Driving the engineered trait by chilling inducible promoter would ensure the minimization of a trade-off between photoprotection and photosynthesis efficiency.