植物激素茉莉酸的代谢及12-羟基茉莉酸在植物抵御昆虫中的功能研究

In response to insect attack, plants rapidly but transiently accumulate large amounts of phytohormone jasmonic acid (JA), which in turn activate defense reactions against insects. Almost all enzymes involved in JA biosynthesis have been discovered，but how JA is metabolized and deactivated is still largely unknown. One of the JA metabolites, jasmonoyl-L-isoleucine (JA-Ile), plays central role in herbivore resistance as a bioactive form of the hormone. However, previous work indicated that JA or its metabolites also function as signals in plant-herbivore interaction independently of JA-Ile. 12-hydroxyjasmonic acid and its sulfated and glucosylated derivatives (collectively referred to 12-OH-JAs) are all JA metabolites that exist in large quantities in many plant species. 12-OH-JAs induce certain physiological responses including potato tuber formation and leaf closing in rain trees, suggesting that these compounds may also play a role in plant-herbivore interactions. To elucidate whether 12-hydroxylation is an important JA metabolic pathway, the time course of accumulations of 12-OH-JAs after insect attack will be determined in a wild tobacco plants, Nicotiana attenuata, and whether 12-OH-JAs are the main forms of JA metabolites will be studied in plants silenced in CYP94B3 gene, a P450 gene which is responsible for the hydroxylation of JA moiety. To further gain insight into the function of 12-OH-JAs in plant-herbivore interactions, bioassays will be performed to examine the changes of insect resistance in plants silenced in CYP94B3, which are deficient in 12-OH-JAs. In addition to expand our knowledge of the catabolism of JA, this study also reveals the function of JA derivatives in plant defense against insects.

植物被昆虫啃食后会快速而短暂地产生大量茉莉酸以调动抵御昆虫的生理反应，这些茉莉酸是如何被代谢和失活的还不清楚。茉莉酸的衍生物JA-Ile是植物抗虫中重要的信号分子，但是本人前期工作证明还有JA-Ile外的其它茉莉酸信号的存在。12-羟基茉莉酸及它的磺基化和糖基化衍生物（统称12-OH-JAs）在多种植物中大量存在，并引起某些生理反应，如诱导马铃薯块茎生成及雨树叶子关闭，说明12-OH-JAs在植物抗虫中可能起作用。为了研究12位羟基化是否为茉莉酸的主要代谢途径，我们将测定野生烟草N. attenuata被昆虫袭击前后12-OH-JAs的含量变化。为了进一步明确12-OH-JAs在植物抗虫中的功能，我们将沉默负责将茉莉酸基团12位碳羟基化的酶，以降低植物中12-OH-JAs的含量并测量植物抗虫能力的变化。本项目不但能加深对茉莉酸代谢途径的理解，也对研究其代谢物在植物抗虫中的功能有重要意义。

植物激素茉莉酸与异亮氨酸的络合物（JA-Ile）是植物被昆虫取食后产生的调控植物防御方应的重要信号物质。由P450家族的94亚族参与的JA-Ile的氧化是其重要的代谢途径。在本研究中，我们克隆到了4个拟南芥CYP94B3基因在野生烟草（Nicotiana attenuata）中的同源基因NaCYP94B3 like-1，-2，-3及-4。独立沉默这四个基因表明NaCYP94B3 like-1及-2参与将JA-Ile的末端12位碳羟基化。共同沉默这两个基因大大降低了植物中羟基化JA-Ile的含量，并增加了JA-Ile的含量，表明其在JA-Ile的代谢中发挥重要作用。同时沉默NaCYP94B3 like-1及-2使植物对广食性昆虫斜纹夜蛾（Spodoptera litura）的抗性大大提高，而这是由于植物中的抗虫次生代谢产物含量增加。我们还发现茉莉酸的受体COI1，通过调控NaCYP94B3 like-1 及 -2的表达，控制JA-Ile的代谢。由于沉默NaCYP94B3 like-1 及 -2并不影响植物的生长发育，该基因可作为通过生物工程提高作物抗性的靶标基因。