A brittle‐2 transgene increases maize yield by acting in maternal tissues to increase seed number

Abstract

The enzyme ADP-glucose pyrophosphorylase is essential for starch biosynthesis and is highly regulated. Here, mutations that increased heat stability and interactions with allosteric effectors were incorporated into the small subunit of the isoform known to be expressed at high levels in the maize endosperm. The resulting variants were transformed into maize with expression targeted to the endosperm. Transgenes harboring the changes increased yield some 35%; however, yield enhancement occurred via an increase in seed number rather than by increased seed weight. Interestingly, seed number increase is controlled by the genotype of the plant rather than the genotype of the seed as seeds increase in number whether or not they contain the transgene as long as the maternal parent has the transgene.The transgene is however expressed in the endosperm, and the altered allosteric and stability properties initially seen in Escherichia coli expression experiments are also seen with the endosperm-expressed gene. The extent of seed number increase is positively correlated with the average daily high temperature during the first 4 days postpollination. While these results were unexpected, they echo the phenotypic changes caused by the insertion of an altered large subunit of this enzyme reported previously (Plant Cell, 24, 2012, 2352. These results call into question some of the reported fundamental differences separating starch synthesis in the endosperm vis-a-vis other plant tissues.abiotic plant stress, ADP-glucose pyrophosphorylase, maize yield, starch synthesis | INTRODUCTIONStarch is the major component of cereal seeds and hence a critical constituent of cereal seed yields. The importance of starch, coupled with the early availability of seminal mutants in important biosynthetic steps, has allowed for a fairly robust understanding of its biochemical pathway (reviewed in Smith, Denyer, & Martin, 1997;Ballicora, Iglesias, & Preiss, 2003;Hannah, 2007;Hannah & Greene, 2008;Hannah & James, 2008;Preiss, 2009;Keeling & Myers, 2010).A series of studies have pointed to the enzyme, ADP-glucose pyrophosphorylase (AGPase) as a key step in this important pathway.AGPase is composed of two identical small and two identical large subunits and synthesizes ADP-glucose from glucose-1-PO 4 and ATP.The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plant physiol.org) is L. Curtis Hannah (lchannah@ufl.edu). inbred B73 and were analyzed in several growing seasons. Complementation of the bt2 mutation was evidenced by a 15 plump: 1 shrunken seed ratio in progeny derived by self-pollination of the F1 generation. The presence of the transgene was monitored by painting a small portion of one leaf with Basta 7 to 10 days postpollination and scoring for resistance 7 days later. Selected transgenic events were also monitored for cosegregation of mutant seed with herbicide sensitivity. All materials for analysis were ...

Fundamental differences in starch synthesis in the maize leaf, embryo, ovary and endosperm

“…These observations are not consistent with the long‐held premise that the BT2 protein functions only in the endosperm and, there, only in the cytosol. Furthermore, recent studies with engineered SH2 and BT2 proteins (Hannah et al ., , ) show that these genes function in the plant to increase seed number. Although the SH2 and BT2 proteins do not contain transit peptides, and hence should be exclusively found in the cytosol, Hennen‐Bierwagen et al .…”

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

“…The expression of maize sh2 AGPase genes in maize (Hannah et al, 2012), rice (Smidansky et al, 2003), and wheat (Smidansky et al, 2002) increased crop yields by increasing the number of grains produced per plant. Analyses of the various GlgC and/or ZmBT1 transgenic plants cultured in growth chambers indicate no significant increases in total seed number or total number of panicles per plant (data not shown).…”

Enhanced sucrose loading improves rice yield by increasing grain size

“…We found that the expression of BEI, AGPL1, and AGPS1, which are involved in storage starch production, was significantly induced in transgenic plants (Supplemental Table S4). AGPase is a key regulatory step in the starch biosynthesis pathway, and its activity strongly affects rice grain yield (Smidansky et al, 2002(Smidansky et al, , 2003Kawagoe et al, 2005;Li et al, 2011b;Hannah et al, 2012). BEI has a specific role in determining the amylopectin fine structure in rice endosperm (Satoh et al, 2003).…”