Lowe Tiffany M, Ailloud Florent, Allen Caitilyn
Mol Plant Microbe Interact. 2015 Mar;28(3):286-97. doi: 10.1094/MPMI-09-14-0292-FI.
Plants produce hydroxycinnamic acid (HCA) defense compounds to combat pathogens, such as the bacterium Ralstonia solanacearum. We showed that an HCA degradation pathway is genetically and functionally conserved across diverse R. solanacearum strains. Further, a feruloyl-CoA synthetase (Δfcs) mutant that cannot degrade HCA was less virulent on tomato plants. To understand the role of HCA degradation in bacterial wilt disease, we tested the following hypotheses: HCA degradation helps the pathogen i) grow, as a carbon source; ii) spread, by reducing HCA-derived physical barriers; and iii) survive plant antimicrobial compounds. Although HCA degradation enabled R. solanacearum growth on HCA in vitro, HCA degradation was dispensable for growth in xylem sap and root exudate, suggesting that HCA are not significant carbon sources in planta. Acetyl-bromide quantification of lignin demonstrated that R. solanacearum infections did not affect the gross quantity or distribution of stem lignin. However, the Δfcs mutant was significantly more susceptible to inhibition by two HCA, namely, caffeate and p-coumarate. Finally, plant colonization assays suggested that HCA degradation facilitates early stages of infection and root colonization. Together, these results indicated that ability to degrade HCA contributes to bacterial wilt virulence by facilitating root entry and by protecting the pathogen from HCA toxicity.
植物会产生羟基肉桂酸(HCA)防御化合物来对抗病原体,如青枯雷尔氏菌。我们发现,一条HCA降解途径在不同的青枯雷尔氏菌菌株中在基因和功能上是保守的。此外,一个无法降解HCA的阿魏酰辅酶A合成酶(Δfcs)突变体在番茄植株上的毒性较低。为了了解HCA降解在青枯病中的作用,我们测试了以下假设:HCA降解有助于病原体:i)作为碳源生长;ii)通过减少HCA衍生的物理屏障进行传播;iii)在植物抗菌化合物中存活。虽然HCA降解能使青枯雷尔氏菌在体外利用HCA生长,但HCA降解对于在木质部汁液和根系分泌物中的生长是可有可无的,这表明HCA在植物体内不是重要的碳源。用乙酰溴对木质素进行定量分析表明,青枯雷尔氏菌感染不会影响茎木质素的总量或分布。然而,Δfcs突变体对两种HCA,即咖啡酸和对香豆酸的抑制作用明显更敏感。最后,植物定殖试验表明,HCA降解促进了感染和根系定殖的早期阶段。总之,这些结果表明,降解HCA的能力通过促进根部侵入和保护病原体免受HCA毒性,从而有助于青枯病的致病性。
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