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.

中文翻译：

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通过对杜鹃花叶子在冷驯化和随时间的脱驯化过程中进行的 RNA-seq 分析揭示，光保护有助于提高耐冻性。

 抽象的

冷驯化（CA）和去驯化（DA）通常伴随着耐冻性（FT）、碳水化合物和激素的变化，对于冬季生存至关重要，尤其是在全球变暖的情况下。由于暖冬和/或非季节性暖期而导致 CA 较弱和 DA 过早的植物很容易因对寒冷的不良反应而受到伤害。因此，了解 FT 的分子机制势在必行。在本研究中，我们使用高通量 RNA-seq 来分析越冬杜鹃“Miyo-no-Sakae”叶片随时间的 CA 和 DA 变化；这些叶子不会休眠，但会在 CA 期间进行光保护，并且在 DA 期间不会生长。使用Mfuzz和加权基因共表达网络分析，我们确定了CA和DA每个阶段的特定转录特征，并提出了涉及共表达基因和生理特征的网络。特别是，我们发现昼夜节律对于获得最强的 FT 至关重要，昼夜节律相关基因的高表达可能与冬季糖分积累有关。此外，常绿叶子在冬季表现出强大的光保护作用，如非光化学猝灭的高值、被注释为“早期光诱导蛋白”的转录本的高表达、粒粒堆积的损失和类囊体的解堆积，所有这些都在DA期间得到缓解。强烈的光保护需求可能是CA过程中脱落酸（ABA）和茉莉酸（JA）含量下降的原因，并且ABA和JA含量的下降可能导致木质素含量的下降。 我们的数据表明，越冬叶片FT的分子机制是独特的，这可能是由于冬季对光保护的高要求所致。