Abstract
The parasitic witchweed Striga hermonthica causes devastating damage to crops in sub-Saharan Africa, yet the mechanism of its parasitism is not well understood. Parasitic plants form a special organ called a haustorium to obtain water and nutrients from host plants. The haustorium is induced by host-derived small molecules, collectively named haustorium-inducing factors (HIFs). The most active HIF known to date is 2,6-dimethoxy-p-benzoquinone (DMBQ), originally isolated from sorghum root extracts. It has been suggested that DMBQ is produced by oxidation of its precursor, syringic acid, and that reactive oxygen species (ROS) and peroxidases are involved in the process. However, the roles of ROS in haustorium formation after HIF recognition remain to be elucidated. Here, we investigated the effects of various inhibitors of ROS and ROS-regulating enzymes on haustorium formation in S. hermonthica. Inhibitors of NADPH oxidases and peroxidases inhibited haustorium formation during treatment with DMBQ, syringic acid, and host root extracts, suggesting that ROS production and/or regulation via NADPH oxidases and peroxidases are essential for haustorium formation. We observed hydrogen peroxide accumulation in the haustorium upon treatment with various HIFs. Our results suggest that ROS and ROS-regulating enzymes are indispensable in downstream signaling of HIFs for haustorium formation.
Highlights
Striga hermonthica, a noxious parasitic plant belonging to the Orobanchaceae family, infects economically important cereals, such as sorghum, maize, pearl millet, and rice, and causes huge damage to world agriculture, especially in sub-Saharan Africa
These results indicate that the ROSscavenger catalase affected haustorium formation in a similar way when induced by either DMBQ or syringic acid
There were slight differences in the inhibitory effect of SOD between DMBQ and syringic acid, it appears that O−2 was necessary for haustorium formation when induced by either haustorium-inducing factors (HIFs)
Summary
A noxious parasitic plant belonging to the Orobanchaceae family, infects economically important cereals, such as sorghum, maize, pearl millet, and rice, and causes huge damage to world agriculture, especially in sub-Saharan Africa. The estimated annual yield losses are over one billion USD, negatively affecting the livelihoods of more than 100 million people (Ejeta, 2007). The infection mechanism of S. hermonthica remains poorly understood and effective control methods for this pest have not yet been established. S. hermonthica is an obligate root parasite, depriving the host plant of water and nutrients. Striga identifies the presence of potential hosts at the time of its germination by recognition of host-derived strigolactones (Yoshida and Shirasu, 2012). The Striga radicle grows toward host roots and forms a special invasive organ, the haustorium, at the tip of its radical
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