Down‐regulation of Glucan, Water‐Dikinase activity in wheat endosperm increases vegetative biomass and yield

Abstract

SummaryA novel mechanism for increasing vegetative biomass and grain yield has been identified in wheat (Triticum aestivum). RNAi-mediated down-regulation of Glucan, Water-Dikinase (GWD), the primary enzyme required for starch phosphorylation, under the control of an endosperm-specific promoter, resulted in a decrease in starch phosphate content and an increase in grain size. Unexpectedly, consistent increases in vegetative biomass and grain yield were observed in subsequent generations. In lines where GWD expression was decreased, germination rate was slightly reduced. However, significant increases in vegetative growth from the two leaf stage were observed. In glasshouse pot trials, down-regulation of GWD led to a 29% increase in grain yield while in glasshouse tub trials simulating field row spacing and canopy development, GWD down-regulation resulted in a grain yield increase of 26%. The enhanced yield resulted from a combination of increases in seed weight, tiller number, spikelets per head and seed number per spike. In field trials, all vegetative phenotypes were reproduced with the exception of increased tiller number. The expression of the transgene and suppression of endogenous GWD RNA levels were demonstrated to be grain specific. In addition to the direct effects of GWD down-regulation, an increased level of a-amylase activity was present in the aleurone layer during grain maturation. These findings provide a potentially important novel mechanism to increase biomass and grain yield in crop improvement programmes.

Analysis of the rice ADPglucose transporter (OsBT1) indicates the presence of regulatory processes in the amyloplast stroma that control ADPglucose flux into starch

“…One possible factor limiting the carbon flux into starch could be simultaneously occurring degradation of starch coupled with synthesis, as observed in GlgC-overexpressing cv Desiree tubers (Sweetlove et al, 1996). Similarly, down-regulation of glucan, water-dikinase, an enzyme that facilitates starch degradation, resulted in enhanced wheat grain yields and increases in biomass (Ral et al, 2012). Hence, increases in starch turnover, which may counterbalance increases in starch synthesis, may be responsible for the absence of any further increases in starch synthesis and accumulation, especially when rice plants are grown under elevated CO 2 conditions.…”

Phosphoglucan-bound structure of starch phosphatase Starch Excess4 reveals the mechanism for C6 specificity

“…Engineered SEX4 could provide a means to generate designer starches with tailored patterns of phosphorylation and physical characteristics useful in industrial settings. Recently, GWD-silenced wheat plants were shown to have a significant increase in starch yield (51), and silencing or engineering SEX4 activity in crop plants may produce similarly favorable results. Elucidation of the structural basis of SEX4 activity provides valuable insights necessary for its application in biotechnology.…”

Cloning and Sequence Analysis of the Nucleotide-Binding Domain of an Alpha-Glucan, Water Dikinase Gene from Cassava (Manihot esculenta Crantz)

“…Similarly, a mutation in a related gene in Arabidopsis, termed sex1, leads to a decrease in the phosphate content of leaf starch (Yu et al, 2001). Downregulation of GWD by RNAi constructs in wheat resulted in increased vegetative biomass and 29% increased grain yield in pot trials (Ral et al, 2012). Also, transgenic Arabidopsis and maize lines engineered to reduce expression of GWD homologues displayed elevated leaf starch content (Weise et al, 2012).…”