Soluble Carbohydrates Regulate Auxin Biosynthesis via PIF Proteins in Arabidopsis    

Abstract

Plants are necessarily highly competitive and have finely tuned mechanisms to adjust growth and development in accordance with opportunities and limitations in their environment. Sugars from photosynthesis form an integral part of this growth control process, acting as both an energy source and as signaling molecules in areas targeted for growth. The plant hormone auxin similarly functions as a signaling molecule and a driver of growth and developmental processes. Here, we show that not only do the two act in concert but that auxin metabolism is itself regulated by the availability of free sugars. The regulation of the biosynthesis and degradation of the main auxin, indole-3-acetic acid (IAA), by sugars requires changes in the expression of multiple genes and metabolites linked to several IAA biosynthetic pathways. The induction also involves members of the recently described central regulator PHYTOCHROME-INTERACTING FACTOR transcription factor family. Linking these three known regulators of growth provides a model for the dynamic coordination of responses to a changing environment.

Nighttime Sugar Starvation Orchestrates Gibberellin Biosynthesis and Plant Growth in Arabidopsis

“…Our experiments revealed the existence of a clear diurnal regulation of KS ( Figure 2B), resulting in enhanced ent-kaurene and GA synthesis at the end of the day (Figures 2C and 2D; see Supplemental Figures 5 and 6 online). In line with this, the rate of auxin biosynthesis at the end of the day has also been shown to be twice that at the beginning of the day (Sairanen et al, 2012). Sugars upregulate auxin biosynthesis (Sairanen et al, 2012), indicating that the synthesis of growth hormones depends on the availability of sugars in order to be able to coordinate growth.…”

“…In line with this, the rate of auxin biosynthesis at the end of the day has also been shown to be twice that at the beginning of the day (Sairanen et al, 2012). Sugars upregulate auxin biosynthesis (Sairanen et al, 2012), indicating that the synthesis of growth hormones depends on the availability of sugars in order to be able to coordinate growth. Attempting hormone-driven growth at a rate exceeding carbon availability is maladaptive and results in severe starvation symptoms (see Supplemental Figure 3B online).…”

“…The evidence that sugar availability affects both auxin (Sairanen et al, 2012) and GA biosynthesis (as outlined in this work) suggests that carbon allocation is key to ensuring a growth pattern that is suited to the plant's environment. This also implies the need to ensure an adequate balance between root and shoot growth.…”

Sugar demand, not auxin, is the initial regulator of apical dominance

“…It would be interesting to determine whether enhanced delivery of sucrose to buds affects auxin biosynthesis, metabolism, and/or conjugation (34)(35)(36) in buds and whether this may have a role in early bud growth. However, our data reveal that it is unlikely that auxin transport plays a role during the early growth period after decapitation.…”

PIFs: Systems Integrators in Plant Development

“…We have chosen to focus mainly on the integration of hormonal signals and the circadian clock. However, there is also evidence that PIFs integrate other pathways that are only briefly mentioned in this review, such as temperature (Koini et al, 2009;Stavang et al, 2009;Kumar et al, 2012) and sugar metabolism Lilley et al, 2012;Sairanen et al, 2012). First, we summarize current knowledge of the PIF-phy interplay regulating morphogenesis.…”