Abstract
Sugarcane contributes more than 70% of sugar production and is the second largest feedstock for ethanol production globally. Since sugar accumulates in sugarcane culms, culm biomass and sucrose content are the most commercially important traits. Despite extensive breeding, progress in both cane yield and sugar content remains very slow in most countries. We hypothesize that manipulating the genetic elements controlling culm growth will alter source-sink regulation and help break down the yield barriers. In this study, we investigate the role of sugarcane ScGAI, an ortholog of SLR1/D8/RHT1/GAI, on culm development and source-sink regulation through a combination of molecular techniques and transgenic strategies. We show that ScGAI is a key molecular regulator of culm growth and development. Changing ScGAI activity created substantial culm growth and carbon allocation changes for structural molecules and storage. ScGAI regulates spatio-temporal growth of sugarcane culm and leaf by interacting with ScPIF3/PIF4 and ethylene signaling elements ScEIN3/ScEIL1, and its action appears to be regulated by SUMOylation in leaf but not in the culm. Collectively, the remarkable culm growth variation observed suggests that ScGAI could be used as an effective molecular breeding target for breaking the slow yield gain in sugarcane.
Highlights
Sugarcane (Saccharum ssp. hybrids) is one of the largest broadacre crops in the world, producing more than 70% of sugar consumed globally
The Arabidopsis DELLA protein AtRGL3 shows an L36F change in this region, which does not prevent its interaction with AtGID1s receptors (Nakajima et al, 2006)
The hydrophobic DELLA and TVHYNP motifs are important for interacting with GA receptors and affecting GA-dependent DELLA degradation (Murase et al, 2008), a recent study confirmed that the DELL amino acid residues are not required for this interaction (Sheerin et al, 2011).The predicted tertiary structure of the DELLA domain from ScGAI showed high molecular spatial similarity to the solved domain structure of the AtGAI protein from Arabidopsis (Fig. 1B)
Summary
Sugarcane (Saccharum ssp. hybrids) is one of the largest broadacre crops in the world, producing more than 70% of sugar consumed globally (http://faostat.fao.org/). Transgenic sugarcane with altered ScGAI expression is hypersensitive to GA and paclobutrazol To gain further insight into the functional role of GA/ScGAI regulation in sugarcane, HpScGAI and ScGAIOE lines and control plants were treated with GA3 (50 μM) or PAC (5 μM), an inhibitor of GA biosynthesis (Supplementary Fig. S8).
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