Characterization of ADP-Glucose Pyrophosphorylase Encoding Genes in Source and Sink Organs of Maize

ADP-glucose pyrophosphorylase catalyzes the first and limiting step in starch biosynthesis. Six cDNA sequences encoding three large subunits and three small subunits of maize AGPase from database were mined and subsequently named: agpl1, agpl2, agpl3, agps1, agps2, and agps3. To elucidate the roles of these isogenes, a comprehensive expression analysis of the gene family was conducted by quantitative real-time RT-PCR. Based on the expression patterns, the six genes can be divided into three groups: (1) steady expressers (agpl1, agps1, and agpl2), which were expressed relatively constantly both in leaf and grain; (2) tissue and development-specific expressers (agpl3 and agps2), which were expressed only in grain at middle and late development phases; (3) tissue-specific expressers (agps3), whose transcripts kept constant during grain filling and were observed only in grain. In order to clarify the effects of sugar and plant hormone on maize AGPase genes expression, a serial of treatments were used. The results showed that AGPase genes significantly differed in response to sugar and hormone inductions. Enormous transcript changes of these genes could be observed in glucose and sucrose treatments. Interestingly, synergistic effect of ABA and sucrose on these genes was observed.