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Article|31 Jan 2022|OPEN
Photoprotection contributes to freezing tolerance as revealed by RNA-seq profiling of Rhododendron leaves during cold acclimation and deacclimation over time.
Bing Liu1 , Fang-Meng Zhao1 , Yan Cao1 , Xiu-Yun Wang1 , Zheng Li1 , Yuanyue Shentu1 , Hong Zhou1 , and Yi-Ping Xia,1 ,
1Genomics and Genetic Engineering Laboratory of Ornamental Plants, College of Agriculture and Biotechnology, Zhejiang University, 866 Yuhangtang Road, Zhejiang 310058, China
*Corresponding author. E-mail: lilyzhou@zju.edu.cn,ypxia@zju.edu.cn

Horticulture Research 9,
Article number: uhab025 (2022)
doi: https://doi.org/10.1093/hr/uhab025
Views: 288

Received: 31 May 2021
Revised: 14 Oct 2021
Accepted: 18 Jan 2022
Published online: 31 Jan 2022

Abstract

Cold acclimation (CA) and deacclimation (DA), which are often accompanied by changes in freezing tolerance (FT), carbohydrates and hormones, are crucial for winter survival, especially under global warming. Plants with weak CA and premature DA caused by warm winters and/or unseasonal warm spells can be easily injured by adverse reactions to cold. Thus, understanding the molecular mechanisms of FT is imperative. In this study, we used high-throughput RNA-seq to profile the CA and DA of leaves of overwintering Rhododendron “Miyo-no-Sakae” over time; these leaves do not undergo dormancy but do undergo photoprotection during CA, and they do not grow during DA. Using Mfuzz and weighted gene coexpression network analysis, we identified specific transcriptional characteristics in each phase of CA and DA and proposed networks involving coexpressed genes and physiological traits. In particular, we discovered that the circadian rhythm is critical for obtaining the strongest FT, and high expression of circadian rhythm-related genes might be linked to sugar accumulation during winter. Furthermore, evergreen leaves exhibited robust photoprotection during winter, as revealed by high values of nonphotochemical quenching, high expression of transcripts annotated as “early light-induced proteins”, loss of granum stacks and destacking of thylakoids, all of which were alleviated during DA. The strong requirement of photoprotection could be the reason for decreased abscisic acid (ABA) and jasmonic acid (JA) contents during CA, and decreases in ABA and JA contents may contribute to decreases in lignin content. Our data suggest that the molecular mechanisms of FT in overwintering leaves are unique, which may be due to the high requirements for photoprotection during winter.