Red light perception by the root is essential for gibberellin-induced primary-root elongation in tomato

Abstract

SummaryThe promoting effect of gibberellin (GA) on primary-root elongation was demonstrated in several species, including Arabidopsis (Arabidopsis thaliana). However, in some other species its effect is less clear.We have used the tomato (Solanum lycopersicum) GA-deficient mutantsgib-1andga 20-oxidase(ga20ox1) to study the role of GA in primary-root elongation and examined the involvement of light in this response.Application of GA togib-1following germination, promoted primary-root elongation, but later, when roots were deeper in the dark, GA had no effect. RNA-seq analysis revealed a typical GA transcriptional response in dark-grown roots, but the output toward cell-expansion was blocked. When dark-grown roots were illuminated deep in the ground, the hormone promoted their elongation. We demonstrated that direct red light to the root is essential for GA-induced elongation. A similar light dependent GA-elongation response was found in wheat (Triticum aestivum) roots, but not in Arabidopsis.We suggest that in tomato GA promotes root elongation following germination when roots are exposed to low light intensity underground, and this contributes to seedling establishment. As root grow deeper into the soil, the insensitivity to GA may be important for continues root growth under fluctuating water availability, as water deficiency suppresses GA accumulation.