Bethke Gerit, Thao Amanda, Xiong Guangyan, Li Baohua, Soltis Nicole E, Hatsugai Noriyuki, Hillmer Rachel A, Katagiri Fumiaki, Kliebenstein Daniel J, Pauly Markus, Glazebrook Jane
Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108
Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108.
Plant Cell. 2016 Feb;28(2):537-56. doi: 10.1105/tpc.15.00404. Epub 2016 Jan 26.
Plant cell walls are important barriers against microbial pathogens. Cell walls of Arabidopsis thaliana leaves contain three major types of polysaccharides: cellulose, various hemicelluloses, and pectins. UDP-D-galacturonic acid, the key building block of pectins, is produced from the precursor UDP-D-glucuronic acid by the action of glucuronate 4-epimerases (GAEs). Pseudomonas syringae pv maculicola ES4326 (Pma ES4326) repressed expression of GAE1 and GAE6 in Arabidopsis, and immunity to Pma ES4326 was compromised in gae6 and gae1 gae6 mutant plants. These plants had brittle leaves and cell walls of leaves had less galacturonic acid. Resistance to specific Botrytis cinerea isolates was also compromised in gae1 gae6 double mutant plants. Although oligogalacturonide (OG)-induced immune signaling was unaltered in gae1 gae6 mutant plants, immune signaling induced by a commercial pectinase, macerozyme, was reduced. Macerozyme treatment or infection with B. cinerea released less soluble uronic acid, likely reflecting fewer OGs, from gae1 gae6 cell walls than from wild-type Col-0. Although both OGs and macerozyme-induced immunity to B. cinerea in Col-0, only OGs also induced immunity in gae1 gae6. Pectin is thus an important contributor to plant immunity, and this is due at least in part to the induction of immune responses by soluble pectin, likely OGs, that are released during plant-pathogen interactions.
植物细胞壁是抵御微生物病原体的重要屏障。拟南芥叶片的细胞壁包含三种主要类型的多糖：纤维素、各种半纤维素和果胶。UDP-D-半乳糖醛酸是果胶的关键组成部分，它由前体UDP-D-葡萄糖醛酸通过葡萄糖醛酸4-表异构酶（GAEs）的作用产生。丁香假单胞菌番茄致病变种ES4326（Pma ES4326）抑制拟南芥中GAE1和GAE6的表达，并且在gae6和gae1 gae6突变体植株中对Pma ES4326的免疫能力受损。这些植株的叶片易碎，叶片细胞壁中的半乳糖醛酸含量较少。在gae1 gae6双突变体植株中，对特定灰葡萄孢分离株的抗性也受到损害。尽管寡聚半乳糖醛酸（OG）诱导的免疫信号在gae1 gae6突变体植株中未改变，但由商业果胶酶、离析酶诱导的免疫信号却减弱了。与野生型Col-0相比，离析酶处理或灰葡萄孢感染从gae1 gae6细胞壁中释放的可溶性糖醛酸更少，这可能反映出OGs更少。虽然OGs和离析酶都能在Col-0中诱导对灰葡萄孢的免疫，但只有OGs能在gae1 gae6中诱导免疫。因此，果胶是植物免疫的重要贡献者，这至少部分归因于可溶性果胶（可能是OGs）在植物-病原体相互作用过程中释放并诱导免疫反应。
