Germinating seedlings and mature shoots of Cuscuta campestris respond differently to light stimuli during parasitism but not during circumnutation

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.

The early dodder gets the host: decoding the coiling patterns of Cuscuta campestris with automated image processing

KEY MESSAGE

We developed an in-house Python-based image analysis pipeline to investigate the movement patterns of Cuscuta. Our analysis unveiled that the coiling and circumnutation movements of Cuscuta are regulated by its intrinsic circadian rhythm. Cuscuta spp., commonly known as dodders, are rootless and leafless stem parasitic plants. Upon germination, Cuscuta starts rotating immediately in a counterclockwise direction (circumnutation) to locate a host plant, creating a seamless vascular connection to steal water and nutrients from its host. In this study, our aim was to elucidate the dynamics of the coiling patterns of Cuscuta, which is an essential step for successful parasitism. Using time-lapse photography, we recorded the circumnutation and coiling movements of C. campestris at different inoculation times on non-living hosts. Subsequent image analyses were facilitated through an in-house Python-based image processing pipeline to detect coiling locations, angles, initiation and completion times, and duration of coiling stages in between. The study revealed that the coiling efficacy of C. campestris varied with the inoculation time of day, showing higher success and faster initiation in morning than in evening. These observations suggest that Cuscuta, despite lacking leaves and a developed chloroplast, can discern photoperiod changes, significantly determining its parasitic efficiency. The automated image analysis results confirmed the reliability of our Python pipeline by aligning closely with manual annotations. This study provides significant insights into the parasitic strategies of C. campestris and demonstrates the potential of integrating computational image analysis in plant biology for exploring complex plant behaviors. Furthermore, this method provides an efficient tool for investigating plant movement dynamics, laying the foundation for future studies on mitigating the economic impacts of parasitic plants.

Rising from the shadows: Selective foraging in model shoot parasitic plants

Despite being sessile, plants nonetheless forage for resources by modulating their growth. Adaptative foraging in response to changes in resource availability and presence of neighbours has strong implications for performance and fitness. It is an even more pressing issue for parasitic plants, which draw resources directly from other plants. Indeed, parasitic plants were demonstrated over the years to direct their growth towards preferred hosts and invest resources in parasitism relative to host quality. In contrast to root parasites that rely mostly on chemical cues, some shoot parasites seem to profit from the ability to integrate different types of abiotic and biotic cues. While significant progress in this field has been made recently, there are still many open questions regarding the molecular perception and the integration of diverse signalling pathways under different ecological contexts. Addressing how different cues are integrated in parasitic plants will be important when unravelling variations in plant interaction pathways, and essential to predict the spread of parasites in natural and agricultural environments. In this review, we discuss this with a focus on Cuscuta species as an emerging parasitic model, and provide research perspectives based on the recent advances in the topic and plant-plant interactions in general.