Exposure to low, non-freezing temperatures develops freezing tolerance in many plant species. Such process is called cold acclimation. Molecular changes undergone during cold acclimation are orchestrated by signalling networks including MAP kinases. Structure and function of chloroplasts are affected by low temperatures. The aim of this work was to study how the MAP kinases MPK3 and MPK6 are involved in the chloroplast performance upon a long period of cold acclimation. We used Arabidopsis thaliana wild type and mpk3 and mpk6 mutants. Adult plants were acclimated during 7 days at 4 °C and then measurements of PSII performance and chloroplast ultrastructure were carried out. Only the mpk6 acclimated plants showed a high freezing sensitivity. No differences in the PSII function were observed in the plants from the three genotypes exposed to non-acclimated or acclimated conditions. The acclimation of wild-type plants produced severe alterations in the ultrastructure of chloroplast and thylakoids, which was more accentuated in the mpk plants. However, only the mpk6 mutant was unable to internalize the damaged chloroplasts into the vacuole. These results indicate that cold acclimation induces alterations in the chloroplast architecture leading to preserve an optimal performance of PSII. MPK3 and MPK6 are necessary to regulate these morphological changes, but besides, MPK6 is needed to the vacuolization of the damaged chloroplasts, suggesting a role in the chloroplast recycling during cold acclimation. The latter could be quite relevant, since it could explain why this mutant is the only one showing an extremely low freezing tolerance.

许多植物物种暴露于低温、非冷冻温度会产生冷冻耐受性。这样的过程称为冷驯化。冷驯化过程中发生的分子变化是由包括 MAP 激酶在内的信号网络协调的。叶绿体的结构和功能受低温影响。这项工作的目的是研究 MAP 激酶 MPK3 和 MPK6 如何参与长期冷驯化后的叶绿体性能。我们使用了拟南芥野生型和mpk3和mpk6突变体。成年植物在 4°C 下适应 7 天，然后进行 PSII 性能和叶绿体超微结构的测量。只有mpk6驯化的植物表现出高度的冷冻敏感性。在来自暴露于非驯化或驯化条件的三种基因型的植物中未观察到 PSII 功能的差异。野生型植物的驯化产生了叶绿体和类囊体超微结构的严重改变，这在mpk植物中更为突出。但是，只有mpk6突变体无法将受损的叶绿体内化到液泡中。这些结果表明冷驯化会引起叶绿体结构的改变，从而保持 PSII 的最佳性能。MPK3 和 MPK6 是调节这些形态变化所必需的，但除此之外，受损叶绿体的空泡化需要 MPK6，这表明在冷驯化过程中叶绿体再循环中起作用。后者可能非常相关，因为它可以解释为什么这个突变体是唯一一个表现出极低冷冻耐受性的突变体。