Changes in cytokinins are sufficient to alter developmental patterns of defense metabolites in Nicotiana attenuata

Abstract

SUMMARYPlant defense metabolites are well known to be regulated developmentally. The optimal defense (OD) theory posits that a t ssue's fitness values and probability of attack should determine defense metabolite allocations. Young leaves are expected to provide a larger fitness value to the plant, and therefore their defense allocations should be higher when compared with older leaves. The mechanisms that coordinate development with defense remain unknown and frequently confound tests of the OD theory predictions. Here we demonstrate that cytokinins (CKs) modulate ontogeny-dependent defenses in Nicotiana attenuata. We found that leaf CK levels highly correlate with inducible defense expressions with high levels in young and low levels in older leaves. We genetically manipulated the developmental patterns of two different CK classes by using senescenceand chemically inducible expression of CK biosynthesis genes. Genetically modifying the levels of different CKs in leaves was sufficient to alter ontogenic patterns of defense metabolites. We conclude that the developmental regulation of growth hormones that include CKs plays central roles in connecting development with defense and therefore in establishing optimal patterns of defense allocation in plants.

Future directions in the ontogeny of plant defence: understanding the evolutionary causes and consequences

“…; Brütting et al . ). Because induced defences have been proposed as a cost‐savings mechanism (Cipollini & Heil ), an ontogenetic shift from induced to constitutive chemical defences could reflect a greater importance of allocation costs early in ontogeny, when plants have the priority to establish and grow to outcompete their neighbouring plants.…”

“…For example in the case of Nicotiana attenuanta , both cytokinins (Brütting et al . ) and ethylene (Diezel et al . ) have been found to regulate the expression of induced defences throughout plant development.…”

“…; Brütting et al . ). The great variation in the ontogenetic trajectories at the whole‐plant level provides an excellent opportunity to assess the causes and consequences of the evolution of changing phenotypes across plant development, which has been scarcely explored.…”

“…Moreover, leaf ontogeny and wholeplant ontogeny may differ markedly in their trajectories of plant defence. Whereas a consistent decrease in secondary chemicals have been found during leaf ontogeny (Koricheva & Barton 2012), much more variable and contrasting ontogenetic trajectories have been reported among species for whole-plant ontogeny (Boege & Marquis 2005;Barton & Koricheva 2010), suggesting different selective pressures and underlying regulatory pathways for organ vs. whole-plant ontogeny (Bowers & Stamp 1993;Diezel et al 2011;Maag et al 2015;Br€ utting et al 2016). The great variation in the ontogenetic trajectories at the whole-plant level provides an excellent opportunity to assess the causes and consequences of the evolution of changing phenotypes across plant development, which has been scarcely explored.…”

Regulation and cell biology of secondary metabolite production in Fusarium graminearum and Fusarium pseudograminearum

“…On the other hand, cytokinins have also been shown to regulate the accumulation of defense metabolites in different plant species (Brütting et al, 2017;Dervinis et al, 2010;Schäfer et al, 2015;Smigocki et al, 1993) which would be counterproductive for the fungus during infection. Thus, it would be very interesting to see if the fungal fusatins are able to only activate certain cytokinin signalling pathways in the plant which are beneficial for the fungus, but are able to avoid those that would induce plant defense responses.…”