Institute of Molecular Biology, Academia Sinica, Taipei, 11529, Taiwan.
New Phytol. 2020 Nov;228(4):1327-1335. doi: 10.1111/nph.16766. Epub 2020 Jul 21.
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.
半乳糖脂单半乳糖基二酰基甘油 (MGDG) 和双半乳糖基二酰基甘油 (DGDG) 分别占叶绿体膜脂质的约 50%和 30%。它们对于光合作用和应激耐受很重要。DGD1 是主要的 DGDG 合成酶，如果发生突变，会严重降低 DGDG 含量并诱导茉莉酸 (JA) 过量产生，导致生长受阻。然而，DGDG 减少如何导致 JA 过量产生尚不清楚。我们将一种诱导型 microRNA（ami-MGD1）引入拟南芥 dgd1 突变体中，以减少 MGDG 的合成，从而进一步降低半乳糖脂的含量，但部分恢复 MGDG：DGDG 比值。我们研究了半乳糖脂和叶绿素含量、JA 生物合成和 JA 响应基因的表达、光系统 II (PSII) 最大量子效率以及叶绿体形状。amiR-MGD1 转化的 dgd1 植物中 JA 生物合成和 JA 响应基因的表达减少。JA 过量产生引起的生长受阻也部分得到挽救，但叶绿素减少和 PSII 损伤与原始 dgd1 突变体相似。叶绿体形状的改变也是 dgd1 观察到的另一个缺陷，但不是由 JA 过量产生引起的，也部分得到挽救。我们的研究结果表明，MGDG：DGDG 比值的增加是 JA 过量产生的主要原因。该比值对于确定叶绿体形状也很重要，而叶绿素和光合作用减少很可能是 DGDG 不足的直接后果。
