Rubisco, which consists of eight large subunits (RBCLs) and eight small subunits (RBCSs), is a major photosynthetic enzyme that is sensitive to chilling stress. However, it is largely unclear how plants maintain high Rubisco content under low temperature conditions. Here, we report that tomato WHIRLY1 (SlWHY1) positively regulates the Rubisco level under chilling stress by directly binding to the promoter region of SlRbcS1, resulting in the activation of SlRbcS1 expression. SlRbcS1-overexpressing lines had higher Rubisco contents and were more resistant to chilling stress compared with the wild type. Quantitative real-time PCR analyses showed that, among the five RbcS genes, only SlRbcS1 expression is up-regulated by chilling treatment. These results indicate that SlWHIRLY1 specifically enhances the levels of SlRbcS1 and confers tolerance to chilling stress. The amino acid sequence of SlRBCS1 shows 92.67% identity with those of another two RBCS proteins and three residues are specifically found in SlRBCS1. However, mutation of these residues to alanine in SlRBCS1 does not influence its function during cold adaptation. Thus, we conclude that high levels of Rubisco, but not the specific residues in SlRBCS1, play important roles in tolerance to chilling stress in tomato.

中文翻译：

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WHIRLY1通过调节低温胁迫下RbcS1的表达来维持番茄叶片的光合作用能力。

Rubisco由八个大亚基（RBCL）和八个小亚基（RBCS）组成，是一种主要的光合作用酶，对低温胁迫敏感。但是，目前尚不清楚植物如何在低温条件下保持高Rubisco含量。在这里，我们报道番茄WHIRLY1（SlWHY1）通过直接结合到SlRbcS1的启动子区域，在寒冷胁迫下积极调节Rubisco的水平，从而激活了SlRbcS1的表达。与野生型相比，过量表达SlRbcS1的品系具有更高的Rubisco含量并且对寒冷胁迫具有更强的抵抗力。实时定量PCR分析显示，在五个Rbc S基因中，只有SlRbcS1表达通过冷处理上调。这些结果表明，SlWHIRLY1特异性增强的水平SlRbcS1并赋予对低温胁迫。SlRBCS1的氨基酸序列与另外两个RBCS蛋白的氨基酸序列显示出92.67％的同一性，并且在SlRBCS1中特异性地发现了三个残基。但是，在冷适应过程中，SlRBCS1中这些残基突变为丙氨酸不会影响其功能。因此，我们得出结论，高水平的Rubisco，而不是SlRBCS1中的特定残基，在番茄抗冷胁迫中起重要作用。