Nighttime gibberellin biosynthesis is influenced by fluctuating environmental conditions and contributes to growth adjustments of Arabidopsis leaves

Abstract

Optimal plant growth performance requires that the action of growth signals, such as gibberellins (GA), are coordinated with the availability of photo-assimilates. Here, we studied the links between gibberellin biosynthesis and carbon availability, and the subsequent effects on growth. The results presented here show that carbon availability, light and dark cues, and the clock ensure the timing and magnitude of gibberellin biosynthesis and that disruption of these mechanisms results in reduced gibberellin levels and expression of downstream genes. Carbon dependent nighttime induction of GIBBERELLIN 3-BETA-DIOXYGENASE 1 (GA3ox1) was severely hampered when preceded by a day of lowered light availability, leading specifically to reduced bioactive GA4 levels, and coinciding with a decline in leaf expansion rate during the night. We attribute this decline in leaf expansion mostly to reduced photo-assimilates. However, plants where gibberellin limitation was alleviated had significantly improved expansion demonstrating the relevance of gibberellins in growth control under varying carbon availability. Carbon dependent expression of upstream gibberellin biosynthesis genes (KAURENE SYNTHASE, KS and GIBBERELLIN 20 OXIDASE 1, GA20ox1) was not translated into metabolite changes within this short timeframe. We propose a model where the extent of nighttime biosynthesis of bioactive GA4 by GA3ox1 is determined by starch, as the nighttime carbon source, and so provides day-to-day adjustment of gibberellin responses.

The Roles of Gibberellins in Regulating Leaf Development

“…A longer photoperiod enhances GA biosynthesis, resulting in a higher expression of the key GA synthesis genes GA20ox and GA3ox , consequently inducing active GAs in Arabidopsis [ 62 ]. In contrast, a lower light availability reduced the expression of GA20ox and GA3ox , resulting in reduced leaf expansion [ 63 , 64 ] and demonstrating that GA20ox and GA3ox are dependent on the intensity and quality of light in Rosa sp. [ 37 ].…”