Seed yield and plant biomass increases in rice are conferred by deregulation of endosperm ADP-glucose pyrophosphorylase

Abstract

In this work we test the hypothesis that yield of rice (Oryza sativa L.) can be enhanced by increasing endosperm activity of ADP-glucose pyrophosphorylase (AGP), a key enzyme in starch biosynthesis. The potential for increases in yield exist because rice initiates more seeds than are taken to maturity and possesses excess photosynthetic capacity that could be utilized if there were more demand for assimilate. Following an approach already shown to be successful in wheat, experiments were designed to increase demand for assimilate by increasing the capacity for starch synthesis in endosperm. This was accomplished by transforming rice with a modified maize AGP large subunit sequence (Sh2r6hs) under control of an endosperm-specific promoter. This altered subunit confers upon AGP decreased sensitivity to allosteric inhibition by inorganic phosphate (Pi) and enhanced heat stability, potentially leading to higher AGP activity in vivo. The Sh2r6hs transgene increased AGP activity in developing endosperm by 2.7-fold in the presence of Pi. Increases in AGP activity in transgenic seeds compared with controls were maximal between 10-15 days after anthesis. Starch content of individual seeds at harvest was not increased, but seed weight per plant and total plant biomass were each increased by more than 20%. Increased endosperm AGP activity thus stimulates setting of additional seeds and overall plant growth rather than increasing yield of seeds already set. Results demonstrate that deregulation of endosperm AGP increases overall plant sink strength, leading to larger, more productive plants in a manner similar to that in wheat having similar genetic modification.

Zea mays iRS1563: A Comprehensive Genome-Scale Metabolic Reconstruction of Maize Metabolism

“…For example, cellulosic biomass yield improvements have been pursued before by altering the lignin content and composition [61], [62], genetically manipulating the cellulose biosynthetic pathway [63] and over-expressing the gene encoding phosphoenolpyruvate carboxylase (PEPC) to improve CO 2 fixation rate [64]. At the same time, grain yield enhancements have been attempted by up-regulating ADP-glucose pyrophosphorylase (AGP) that catalyzes the rate limiting step in starch synthesis [65].…”

Starch

“…Interestingly, a similar study using the potato cultivar Desiree failed to elevate net starch accumulation (Sweetlove et al 1996). Unexpectedly, expression of AGPase genes under the control of putative endosperm-specific promoters also increased the total number of maize kernels on individual cobs (Hannah et al 2012) and number of developing grains per rice panicle or wheat head (Smidansky et al 2002(Smidansky et al , 2003Meyer et al 2004). The basis for the differences seen between these two studies is not clear although the use of different potato cultivars and their corresponding differences in starch content is a likely factor.…”

Towards Regional, Error-Bounded Landscape Carbon Storage Estimates for Data-Deficient Areas of the World

“…temperate grasslands). For some agricultural land covers, yield data were more widely available and these were converted to standing crop biomass using published equations [40]–[42], the exception being sugarcane, where almost the entire crop is utilised (so annual yield was assumed to be equal to the aboveground live biomass). In total, 45 published papers fulfilled the search criteria (Table 3, Table S2, Table S3, References S1).…”