Instituto de Recursos Naturales y Agrobiologia de Salamanca (IRNA SA-CSIC), Salamanca, Spain.
Plant Signal Behav. 2011 Dec;6(12):1937-42. doi: 10.4161/psb.6.12.18264.
Can Arabidopsis cell suspension cultures (ACSC) provide a useful working model to investigate genetically-controlled defense responses with signaling cascades starting in chloroplasts? In order to provide a convincing answer, we analyzed the early transcriptional profile of Arabidopsis cells at high light (HL). The results showed that ACSC respond to HL in a manner that resembles the singlet oxygen ((1)O(2))-mediated defense responses described for the conditional fluorescent (flu) mutant of Arabidopsis thaliana. The flu mutant is characterized by the accumulation of free protochlorophyllide (Pchlide) in plastids when put into darkness and the subsequent production of (1)O(2) when the light is on. In ACSC, (1)O(2) is produced in chloroplasts at HL when excess excitation energy flows into photosystem II (PSII). Other reactive oxygen species are also produced in ACSC at HL, but to a lesser extent. When the HL stress ceases, ACSC recovers the initial rate of oxygen evolution and cell growth continues. We can conclude that chloroplasts of ACSC are both photosynthetically active and capable of initiating (1)O(2)-mediated signaling cascades that activate a broad range of genetically-controlled defense responses. The upregulation of transcripts associated with the biosynthesis and signaling pathways of OPDA (12-oxophytodienoic acid) and ethylene (ET) suggests that the activated defense responses at HL are governed by these two hormones. In contrast to the flu mutant, the (1)O(2)-mediated defense responses were independent of the upregulation of EDS1 (enhanced disease susceptibility) required for the accumulation of salicylic acid (SA) and genetically-controlled cell death. Interestingly, a high correlation in transcriptional expression was also observed between ACSC at HL, and the aba1 and max4 mutants of Arabidopsis, characterized by defects in the biosynthesis pathways of abscisic acid (ABA) and strigolactones, respectively.
拟南芥细胞悬浮培养（ACSC）能否为研究从叶绿体开始的遗传控制防御反应的信号级联提供有用的工作模型？为了提供令人信服的答案，我们分析了高光（HL）下拟南芥细胞的早期转录谱。结果表明，ACSC 以类似于拟南芥条件荧光（flu）突变体中描述的单线态氧（1O2）介导的防御反应的方式对 HL 做出反应。flu 突变体的特征是当置于黑暗中时质体中游离原叶绿素酸酯（Pchlide）的积累，以及当光照时 1O2 的产生。在 ACSC 中，当过量的激发能流入光系统 II（PSII）时，在 HL 下叶绿体中会产生 1O2。在 HL 下，ACSC 还会产生其他活性氧，但程度较小。当 HL 应激停止时，ACSC 恢复初始氧释放速率，细胞生长继续。我们可以得出结论，ACSC 的叶绿体既具有光合作用活性，又能够启动 1O2 介导的信号级联，从而激活广泛的遗传控制防御反应。与 flu 突变体不同，OPDA（12-氧代植物二烯酸）和乙烯（ET）生物合成和信号通路相关转录物的上调表明，HL 下激活的防御反应受这两种激素的控制。与 flu 突变体不同，1O2 介导的防御反应不依赖于 EDS1（增强的疾病易感性）的上调，EDS1 是水杨酸（SA）积累和遗传控制细胞死亡所必需的。有趣的是，HL 下的 ACSC 与拟南芥的 aba1 和 max4 突变体之间也观察到转录表达的高度相关性，这两个突变体分别在脱落酸（ABA）和独脚金内酯的生物合成途径中存在缺陷。
