Petunia as model for elucidating adventitious root formation and mycorrhizal symbiosis: at the nexus of physiology, genetics, microbiology and horticulture

Abstract

Adventitious root formation in cuttings and establishment of arbuscular mycorrhizal symbiosis reflect the enormous plasticity of plants and are key factors in the efficient and sustainable clonal propagation and production of ornamental crops. Based on the high importance of Petunia hybrida for the European and US annual bedding plant markets and its suitability as a model for basic plant sciences, petunia has been established as an experimental system for elucidating the molecular and physiological processes underlying adventitious root formation and mycorrhizal symbiosis. In the present review, we introduce the tools of the Petunia model system. Then, we discuss findings regarding the hormonal and metabolic control of adventitious rooting in the context of diverse environmental factors as well as findings on the function of arbuscular mycorrhiza related to nutrient uptake and resistance to root pathogens. Considering the recent publication of the genomes of the parental species of P. hybrida and other tools available in the petunia scientific community, we will outline the quality of petunia as a model for future system-oriented analysis of root development and function in the context of environmental and genetic control, which are at the heart of modern horticulture.

Reprogramming of Cell Fate During Root Regeneration by Transcriptional and Epigenetic Networks

“…Depending on the status of the AR source cells, they can be directly fate-converted to AR root founder cells by a rootinducing signal or they first have to acquire root competence involving dedifferentiation . The natural ability of plants to regenerate is widely used in tissue culture, modern horticulture, and agriculture (Sussex, 2008;Druege and Franken, 2019). In rice and other cereals, ARs represent the main components of the root system as the primary root originating from the embryonic RAM is short-lived.…”

Ericoid mycorrhizal fungus enhances microcutting rooting of Rhododendron fortunei and subsequent growth

“…JAs serve as a wound signal during AR formation, and they can be accumulated in plant tissues just a few minutes after wounding. It has been proposed that increased JA concentration promotes the formation of ARs in cuttings through accumulation of IAA in the base of stems and/or canalization towards AR source cells 4 . Felten et al (2010) 51 suggested that JA might act a molecular signal for inducing lateral roots.…”

“…The formation of ARs is a complex process, which can be affected by multiple factors including genetics, age, endogenous hormones, and nutritional status of plants or plant organs to be used for cutting, as well as rooting environments, such as temperature, light, relative humidity, soil or substrate properties, and soil microbes 5,6 . Thus far, how plant endogenous clues interact with environmental factors in inducing AR formation is still poorly understood even though significant progress in molecular basis on AR formation has been made recently 4,7 . Natural auxin, indole-3-acetic acid (IAA) plays fundamental roles in AR formation 8 .…”

“…ARs are also economically important as propagation through cuttings is central to many horticultural and forest crops 2 . Many popular ornamental crops are vegetatively propagated due to the formation ARs from various cuttings 3 , a process essential to provide several billion rooted ornamental plants to the European 4 and the United States (U.S.) 5 markets each year. Moreover, the formation of ARs permits clonal propagation of desirable genotypes and sports for commercial production or rapid fixation of breeding lines for crop improvement 6 .…”

“…In plant propagation by cuttings, it is recommended that maximum benefits from AM fungal symbiosis can be achieved if inoculum is present during AR formation. However, mechanisms underlying AM fungus-mediated AR formation are largely uncertain 4 , 17 , 25 .…”