Abstract
Plants have a remarkable regenerative capacity, which allows them to survive tissue damage after biotic and abiotic stresses. In this study, we use Solanum lycopersicum ‘Micro-Tom’ explants as a model to investigate wound-induced de novo organ formation, as these explants can regenerate the missing structures without the exogenous application of plant hormones. Here, we performed simultaneous targeted profiling of 22 phytohormone-related metabolites during de novo organ formation and found that endogenous hormone levels dynamically changed after root and shoot excision, according to region-specific patterns. Our results indicate that a defined temporal window of high auxin-to-cytokinin accumulation in the basal region of the explants was required for adventitious root formation and that was dependent on a concerted regulation of polar auxin transport through the hypocotyl, of local induction of auxin biosynthesis, and of local inhibition of auxin degradation. In the apical region, though, a minimum of auxin-to-cytokinin ratio is established shortly after wounding both by decreasing active auxin levels and by draining auxin via its basipetal transport and internalization. Cross-validation with transcriptomic data highlighted the main hormonal gradients involved in wound-induced de novo organ formation in tomato hypocotyl explants.
Highlights
IntroductionDuring indirect tissue-culture regeneration, the sequential incubation of tissue explants on different hormone-supplemented media reprograms some cells to form new organs (i.e., roots, shoots, or embryos) via specific downstream transcriptional networks [3,4]
To characterize the regenerative capacity of hypocotyl fragments without the shoot (Figure 1a), we quantified the extent of de novo shoot formation and found that higher regeneration levels were observed on the apical region of fragments that already included the most basal region of the hypocotyl, irrespectively of the length of the explants (Figure 1b,c)
Our results suggest that local CK biosynthesis in the basal region of the ‘Micro-Tom’ hypocotyl explants plays an inhibitory role in adventitious root (AR) induction by restricting auxin-induced formative responses to a defined region near the wounding
Summary
During indirect tissue-culture regeneration, the sequential incubation of tissue explants on different hormone-supplemented media reprograms some cells to form new organs (i.e., roots, shoots, or embryos) via specific downstream transcriptional networks [3,4]. Excision-induced adventitious root (AR) formation in detached leaves has been intensively studied, and some of the hormonal and transcriptional networks that are involved in this process have been recently identified [5,6]. In both experimental systems though, the establishment of differential hormone-responsive patterns across the regeneration zone of the explants is critical for de novo organ initiation [7]
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