Functions of maize genes encoding pyruvate phosphate dikinase in developing endosperm

Area of Science:

• Plant Biology
• Biochemistry
• Genetics

Background:

• Maize (Zea mays) opaque2 (o2) mutations enhance endosperm nutritional value but cause detrimental pleiotropic effects.
• The bZIP transcriptional regulator Opaque2 (O2) directly targets genes encoding pyruvate phosphate dikinase (PPDK), an enzyme with diverse roles in plants.

Purpose of the Study:

• To investigate the function of PPDK in maize starchy endosperm during grain filling.
• To determine if PPDK plays a role in the opaque phenotype associated with o2 mutations.

Main Methods:

• Individual inactivation of maize PPDK genes (pdk1 and pdk2) using transposon insertions.
• Endosperm-specific RNA interference (RNAi) to simultaneously target pdk1 and pdk2.
• Analysis of kernel weight, endosperm composition, PPDK activity, and metabolic intermediates.

Main Results:

• PPDK is highly abundant in maize endosperm during grain fill, with pdk2 encoding the majority of this enzyme.
• Complete PPDK knockout via RNAi resulted in an opaque kernel phenotype, similar to o2 mutations, without affecting overall kernel weight or storage compound synthesis.
• PPDK knockout led to elevated glycolytic intermediates, altered energy charge, and smaller, more numerous starch granules.

Conclusions:

• Pyruvate phosphate dikinase (PPDK) is crucial for normal maize endosperm metabolism and contributes to the opaque phenotype.
• Opaque2 mutations may influence the opaque phenotype not only through storage protein regulation but also by affecting PPDK expression.