The Role of Endogenous Strigolactones and Their Interaction with ABA during the Infection Process of the Parasitic Weed Phelipanche ramosa in Tomato Plants

Abstract

The root parasitic plant species Phelipanche ramosa, branched broomrape, causes severe damage to economically important crops such as tomato. Its seed germination is triggered by host-derived signals upon which it invades the host root. In tomato, strigolactones (SLs) are the main germination stimulants for P. ramosa. Therefore, the development of low SL-producing lines may be an approach to combat the parasitic weed problem. However, since SLs are also a plant hormone controlling many aspects of plant development, SL deficiency may also have an effect on post-germination stages of the infection process, during the parasite-host interaction. In this study, we show that SL-deficient tomato plants (Solanum lycopersicum; SlCCD8 RNAi lines), infected with pre-germinated P. ramosa seeds, display an increased infection level and faster development of the parasite, which suggests a positive role for SLs in the host defense against parasitic plant invasion. Furthermore, we show that SL-deficient tomato plants lose their characteristic SL-deficient phenotype during an infection with P. ramosa through a reduction in the number of internodes and the number and length of secondary branches. Infection with P. ramosa resulted in increased levels of abscisic acid (ABA) in the leaves and roots of both wild type and SL-deficient lines. Upon parasite infection, the level of the conjugate ABA-glucose ester (ABA-GE) also increased in leaves of both wild type and SL-deficient lines and in roots of one SL-deficient line. The uninfected SL-deficient lines had a higher leaf ABA-GE level than the wild type. Despite the high levels of ABA, stomatal aperture and water loss rate were not affected by parasite infection in the SL-deficient line, while in wild type tomato stomatal aperture and water loss increased upon infection. Future studies are needed to further underpin the role that SLs play in the interaction of hosts with parasitic plants and which other plant hormones interact with the SLs during this process.

Low infection of Phelipanche aegyptiaca in Micro-Tom mutants deficient in CAROTENOID CLEAVAGE DIOXYGENASE 8

“…Probably, small amounts of SLs were produced in roots of the RNAi lines and causes the infection of P. ramosa. Yet these lines are more prone to infection by pre-germinated P. ramosa and the parasite develops faster than in WT, suggesting a positive role of SLs in host defense against parasitic plant infection [47]. The reduced levels of defense-related hormones such as jasmonic, salicylic, and abscisic acids in the SlCCD8 RNAi lines [48] may contribute to their increased susceptibility to parasite infection.…”

Distinct roles for strigolactones in cyst nematode parasitism of Arabidopsis roots

“…SLs induce the germination of parasitic plants, but also seem to play a role in the regulation of the attachment, possibly through an effect on the establishment of a xylem bridge inside the root vasculature for the uptake of nutrients (Heide-Jørgensen and Kuijt 1995;Jamil et al 2011). Indeed, a tomato strigolactone mutant that was infected with pregerminated Phelipanche ramosa seeds displayed a lower resistance towards infection showing that strigolactones positively affect resistance (Cheng et al 2017). This is consistent with the better development of females in the max2-1 and max4-1 mutants of Arabidopsis as found in the present study.…”

Identification of seeds ofPhelipanche ramosa,Phelipanche muteliiandOrobanche cumanain the soils from different agricultural regions in Bulgaria by molecular markers

“…The first critical step is germination and it is regulated by chemicals emitted from the roots of prospective host plants [9,10]. With some exceptions like sorgoleone, the chemical signals belong to the so-called strigolactones, which also play role in communication and attraction of beneficial arbuscular mycorrhizal fungi [11][12][13]. Parasites take advantage of this system and use it to recognize prospective hosts [13,14].…”