Integrating the Roles for Cytokinin and Auxin in De Novo Shoot Organogenesis: From Hormone Uptake to Signaling Outputs

Abstract

De novo shoot organogenesis (DNSO) is a procedure commonly used for the in vitro regeneration of shoots from a variety of plant tissues. Shoot regeneration occurs on nutrient media supplemented with the plant hormones cytokinin (CK) and auxin, which play essential roles in this process, and genes involved in their signaling cascades act as master regulators of the different phases of shoot regeneration. In the last 20 years, the genetic regulation of DNSO has been characterized in detail. However, as of today, the CK and auxin signaling events associated with shoot regeneration are often interpreted as a consequence of these hormones simply being present in the regeneration media, whereas the roles for their prior uptake and transport into the cultivated plant tissues are generally overlooked. Additionally, sucrose, commonly added to the regeneration media as a carbon source, plays a signaling role and has been recently shown to interact with CK and auxin and to affect the efficiency of shoot regeneration. In this review, we provide an integrative interpretation of the roles for CK and auxin in the process of DNSO, adding emphasis on their uptake from the regeneration media and their interaction with sucrose present in the media to their complex signaling outputs that mediate shoot regeneration.

Comprehensive Phytohormone Profiling of Kohlrabi during In Vitro Growth and Regeneration: The Interplay with Cytokinin and Sucrose

“…A correlation analysis between the level of endogenous phytohormones in the later DNSO phase and the regeneration potential of different kohlrabi explant types revealed that even in the absence of CIM, high endogenous auxin levels (and, more importantly, a high auxin/CK ratio) can be sufficient to induce callus formation, suggesting that the content of endogenous phytohormones is crucial for the induction of morphogenic events, rather than the composition of the culture media [ 36 ]. This finding raised the importance of another inadequately addressed issue in plant tissue culture: the relationship between exogenous application and endogenous phytohormone levels and the importance of phytohormone uptake from the media [ 45 ]. Equally important, subsequent studies found a significant effect of CK and sucrose treatments, including their interaction, in the course of kohlrabi DNSO, with a prominent increase in total endogenous CK levels after joint application of 2 mg L −1 trans Z and 9% sucrose, indicating possible involvement of sucrose in CK homeostasis and uptake [ 39 ].…”

“…Plant explants have previously been shown to be able to take up CKs from the in vitro growth medium, which consequently influence the endogenous content of CKs as well as other groups of phytohormones [ 73 ]. CK uptake by explants during DNSO is not yet fully elucidated, but it can be assumed to depend on several groups of CK transporters (reviewed in [ 45 ]).…”

Molecular farming: Expanding the field of edible vaccines for sustainable fish aquaculture

“…Consequently, the growth of non‐transgenic plants is eliminated by adding antibiotics (hygromycin, kanamycin, spectinomycin) or herbicides (Basta) into a selective medium containing micro‐ and macronutrients 126–128 . Plantlet regeneration is then achieved through somatic embryogenesis or de novo organogenesis modulated by plant hormones (auxins and cytokinins) 154,155 followed by confirmation of transgene presence by genotyping. Considering the chloroplast transformation in multicellular plants, repeated rounds of propagation and selection are needed for the eventual regeneration of homoplasmic plants (all copies of the plastome are transformed) 152 …”

Gene expression profiling before and after internode culture for adventitious shoot formation in ipecac

“…The balance of exogenously applied auxin and cytokinin (CK) concentrations affects organogenesis: a high ratio of auxin to CK induces adventitious roots, a low ratio induces adventitious shoots, and a high concentration of both hormones induces callus [ 5 ]. In general, de novo shoot and root organogenesis require the addition of phytohormones, such as auxin and CK, into the culture media in plant tissue culture [ 6 ].…”