• Galactolipids monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG) constitute c. 50% and c. 30% of chloroplast membrane lipids, respectively. They are important for photosynthesis and stress tolerance. Mutations in DGD1, the major DGDG‐synthesizing enzyme, severely reduce DGDG content and induce jasmonic acid (JA) overproduction, resulting in stunted growth. However, how DGDG reduction leads to JA overproduction is unknown.
• We introduced an inducible microRNA (ami‐MGD1) into an Arabidopsis dgd1 mutant to reduce MGDG synthesis, thereby further diminishing galactolipid content, but partially restoring the MGDG : DGDG ratio. Galactolipid and Chl contents, expression of JA‐biosynthesis and JA‐responsive genes, photosystem II (PSII) maximum quantum efficiency, and chloroplast shape were investigated.
• Expression of JA‐biosynthesis and JA‐responsive genes were reduced in amiR‐MGD1‐transformed dgd1 plants. Stunted growth caused by JA overproduction was also partially rescued, but Chl reduction and PSII impairment remained similar to the original dgd1 mutant. Altered chloroplast shape, which is another defect observed in dgd1 but is not caused by JA overproduction, was also partially rescued.
• Our results reveal that an increased MGDG : DGDG ratio is the primary cause of JA overproduction. The ratio is also important for determining chloroplast shapes, whereas reduced Chl and photosynthesis are most likely a direct consequence of insufficient DGDG.

中文翻译：

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半乳糖脂MGDG：DGDG的比例增加会引起茉莉酸的过量生产并改变叶绿体的形状。

• 半乳糖脂单半乳糖基二酰基甘油（MGDG）和二半乳糖基二酰基甘油（DGDG）构成c。50％和c。叶绿体膜脂质分别占30％。它们对于光合作用和胁迫耐受性很重要。DDG1（主要的DGDG合成酶）中的突变会严重降低DGDG含量并诱导茉莉酸（JA）过量生产，从而导致生长受阻。但是，降低DGDG导致JA过量生产的方法尚不清楚。
• 我们将可诱导的microRNA（ami‐MGD1）引入拟南芥dgd1突变体中以减少MGDG的合成，从而进一步减少半乳糖脂的含量，但部分恢复了MGDG：DGDG的比例。研究了半乳糖脂和Chl的含量，JA生物合成和JA反应基因的表达，光系统II（PSII）的最大量子效率以及叶绿体的形状。
• 在amiR‐MGD1转化的dgd1植物中，JA生物合成和JA反应基因的表达降低。由JA过量生产引起的发育不良生长也得到部分挽救，但Chl降低和PSII损伤仍与原始dgd1突变体相似。叶绿体形状的改变（部分是dgd1中观察到的另一个缺陷，但不是由JA过量生产引起的）也得到了部分挽救。
• 我们的结果表明，增加的MGDG：DGDG比率是JA生产过剩的主要原因。该比率对于确定叶绿体形状也很重要，而降低的Chl和光合作用很可能是DGDG不足的直接结果。