AUTHOR=Liu Qianhe , Jones Chris S. , Parsons Anthony J. , Xue Hong , Rasmussen Susanne 

TITLE=Does gibberellin biosynthesis play a critical role in the growth of Lolium perenne? Evidence from a transcriptional analysis of gibberellin and carbohydrate metabolic genes after defoliation

JOURNAL=Frontiers in Plant Science

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.00944

DOI=10.3389/fpls.2015.00944

ISSN=1664-462X

ABSTRACT=<p>Global meat and milk production depends to a large extent on grazed pastures, with <italic>Lolium perenne</italic> being the major forage grass in temperate regions. Defoliation and subsequent regrowth of leaf blades is a major and essential event with respect to <italic>L. perenne</italic> growth and productivity. Following defoliation, carbohydrates (mainly fructans and sucrose) have to be mobilized from heterotrophic tissues to provide energy and carbon for regrowth of photosynthetic tissues. This mobilization of reserve carbohydrates requires a substantial change in the expression of genes coding for enzymes involved in carbohydrate metabolism. Here we tested the hypothesis that gibberellins (GA) are at the core of the processes regulating the expression of these genes. Thus, we examined the transcript profiles of genes involved in carbohydrate and GA metabolic pathways across a time course regrowth experiment. Our results show that following defoliation, the immediate reduction of carbohydrate concentrations in growing tissues is associated with a concomitant increase in the expression of genes encoding carbohydrate mobilizing invertases, and was also associated with a strong decrease in the expression of fructan synthesizing fructosyltransferase genes. We also show that the decrease in fructan levels is preceded by increased expression of the GA activating gene <italic>GA</italic><sub>3</sub>-<italic>oxidase</italic> and decreased expression of the GA inactivating gene <italic>GA</italic><sub>2</sub><italic>-oxidase</italic> in sheaths. <italic>GA</italic><sub>3</sub>-<italic>oxidase</italic> expression was negatively, while <italic>GA</italic><sub>2</sub><italic>-oxidase</italic> positively linked to sucrose concentrations. This study provides indicative evidence that gibberellins might play a role in <italic>L. perenne</italic> regrowth following defoliation and we hypothesize that there is a link between gibberellin regulation and sugar metabolism in <italic>L. perenne</italic>.</p>