Involvement of MID1-COMPLEMENTING ACTIVITY 1 encoding a mechanosensitive ion channel in prehaustorium development of the stem parasitic plant Cuscuta campestris.

Parasitic plants pose a substantial threat to agriculture as they attack economically important crops. The stem parasitic plant Cuscuta campestris invades the host's stem with a specialized organ referred to as the haustorium, which absorbs nutrients and water from the host. Initiation of the parasitic process in C. campestris requires mechanical stimuli to its stem. However, the mechanisms by which C. campestris perceives mechanical stimuli are largely unknown. Previous studies have shown that mechanosensitive ion channels (MSCs) are involved in the perception of mechanical stimuli. To examine if MSCs are involved in prehaustorium development upon tactile stimuli, we treated C. campestris plants with an MSC inhibitor, GsMTx-4, which resulted in a reduced density of prehaustoria. To identify the specific MSC gene involved in prehaustorium development, we analyzed the known functions and expression patterns of Arabidopsis MSC genes and selected MID1-COMPLEMENTING ACTIVITY 1 (MCA1) as a primary candidate. The MSC activity of CcMCA1 was confirmed by its ability to complement the phenotype of a yeast mid1 mutant. To evaluate the effect of CcMCA1 silencing on prehaustorium development, we performed host-induced gene silencing using Nicotiana tabacum plants that express an artificial microRNA-targeting CcMCA1. In the CcMCA1-silenced C. campestris, the number of prehaustoria per millimeter of stem length decreased, and the interval length between prehaustoria increased. Additionally, the expression levels of known genes involved in prehaustorium development, such as CcLBD25, decreased significantly in the CcMCA1-silenced plants. The results suggest that CcMCA1 is involved in prehaustorium development in C. campestris.