A host-free transcriptome for early haustorium development in Cuscuta campestris

When exposed to far red (FR) light in the presence of a tactile stimulus, apical portions of Cuscuta campestris stems develop haustoria that in their early stages bear many of the characteristics of naturally developing haustoria. The first visual sign appears after one to two days with a slight bump where the otherwise flat epidermal cells appear rounded on the surface. This early infective 'swelling stage' (SWE), soon becomes more pronounced and culminates in a macroscopically visible structure of 1-2 mm that begins to stick to the surface it faces ('attaching stage' (ATT)). In the center of this lateral structure, the haustorium finally emerges and the adhesive surface forms a ring around it. On a host, the split in the sticky adhesive ring together with the action of degrading enzymes causes a rupture in the infected tissue and the intrusion of the haustorium that will then begin to feed. In the host-free system used here to induce haustoria, this is the final stage that can be observed and will be referred to as the 'penetrating stage' (PEN). FR-exposed stem sections below and above the region where haustoria developed ('non-infective stems' (niS)) (with no visual changes in morphology) were used as reference sites. Twelve samples (triplicates of the aforementioned three infective and one non-infective tissue types) were collected for sequencing and a total of ca. 375M raw reads for all libraries was generated.