Disruption of a rice gene for α-glucan water dikinase, OsGWD1, leads to hyperaccumulation of starch in leaves but exhibits limited effects on growth

Abstract

To identify potential regulators of photoassimilate partitioning, we screened for rice mutant plants that accumulate high levels of starch in the leaf blades, and a mutant line leaf starch excess 1 (LSE1) was obtained and characterized. The starch content in the leaf blades of LSE1 was more than 10-fold higher than that in wild-type plants throughout the day, while the sucrose content was unaffected. The gene responsible for the LSE1 phenotype was identified by gene mapping to be a gene encoding α-glucan water dikinase, OsGWD1 (Os06g0498400), and a 3.4-kb deletion of the gene was found in the mutant plant. Despite the hyperaccumulation of starch in their leaf blades, LSE1 plants exhibited no significant change in vegetative growth, presenting a clear contrast to the reported mutants of Arabidopsis thaliana and Lotus japonicus in which disruption of the genes for α-glucan water dikinase leads to marked inhibition of vegetative growth. In reproductive growth, however, LSE1 exhibited fewer panicles per plant, lower percentage of ripened grains and smaller grains; consequently, the grain yield was lower in LSE1 plants than in wild-type plants by 20~40%. Collectively, although α-glucan water dikinase was suggested to have universal importance in leaf starch degradation in higher plants, the physiological priority of leaf starch in photoassimilate allocation may vary among plant species.

The OsMYB30 Transcription Factor Suppresses Cold Tolerance by Interacting with a JAZ Protein and Suppressing β-Amylase Expression

“…A previous study reported that starch content and soluble sugars in leaves were responsive to various environmental stresses, but the complex starch synthesis and degradation processes were not completely revealed (Lu et al, 2005;Lu and Sharkey, 2006), and only a few studies on starch degradation were reported in rice (Kitajima et al, 2009;Yun et al, 2011;Hakata et al, 2012;Hirose et al, 2013). With the discovery of the maltose transporter MEX1, researchers considered that maltose was one of the predominant forms that was exported to the cytosol for further metabolism (Niittylä et al, 2004;Lu et al, 2005;Lu and Sharkey, 2006), and the key role in starch digestion was attributed to b-amylase (BMY; Orzechowski, 2008).…”

Genetic engineering of transitory starch accumulation by knockdown of OsSEX4 in rice plants for enhanced bioethanol production

“…Glucan, water dikinase (GWD), and SEX4 are required for the breakdown of leaf starch in Arabidopsis (Caspar et al, 1991; Zeeman et al, 1998). In cereals, knockdown or knockout of GWD expression in maize (Weise et al, 2012) and rice (Hirose et al, 2013) result in increased leaf starch contents. Weise et al (2012) reported that transgenic maize expressing a putative SEX4 RNAi construct did not show increased leaf starch contents.…”

“…This finding is consistent with the observation that knockdown expression of GWD in transgenic maize plants increases the leaf starch content and does not affect phenotypes associated with plant biomass production and plant morphology (Weise et al, 2012). Moreover, a rice GWD mutant shows defective leaf starch degradation, but vegetative growth is unaffected (Hirose et al, 2013). Thus, degradation of leaf starch during the dark period is not critical for vegetative growth in cereal plants, whereas the growth of Arabidopsis plants is affected.…”

“…Cereal crops also produce GWD, PWD, and SEX4 proteins. Studies of cereal plants demonstrate that GWD functions in the degradation of transitory starch (Chen et al, 2018; Hirose et al, 2013; Weise et al, 2012). However, the mechanism of transitory starch degradation in cereal plants remains unclear, and some reports indicate that it differs from that in Arabidopsis.…”

Suppression of glucan, water dikinase in the endosperm alters wheat grain properties, germination and coleoptile growth

“…Similar fertility effects were seen in a study of Lotus japonicus L. GWD mutants (Vriet et al ., ). Constitutive expression of a GWD RNAi construct in maize ( Zea mays L.) or rice ( Oryza sativa L.) reduced the endogenous GWD expression and produced a leaf starch excess with no associated biomass or growth rate reduction (Hirose et al ., ; Weise et al ., ). However, while there is strong evidence for the importance of GWD in transient (leaf) starch metabolism, there is as yet no strong evidence for its importance in storage starch synthesis.…”