combinatorial interaction of two adjacent cisactive promoter regions mediates the synergistic induction of bt2 gene by sucrose and aba in maize endosperm the accumulation of starch in cereal endosperm is a key process that determines crop yield and quality research has reported that sucrose and abscisic acid aba synergistically regulate the synthesis of crop starch however little is known about the molecular mechanisms behind this synergistic effect in this study the effect of sucrose and aba on starch synthesis in maize endosperm was investigated the starch content the adpglc pyrophosphorylase agpase concentration and the expression of agpaseencoding genes were found to be enhanced slightly by sucrose or aba alone but were elevated significantly by the cotreatment of sucrose and aba truncation analysis of the bt2 promoter via transient expression in maize endosperm showed that the promoter region 370186 is involved in sucrose response and that an adjacent region 18643 responds to aba the synergistic induction of sucrose and aba on bt2 promoter activity requires interaction with both of these regions interestingly removal of the sucroseresponsive region 370 to 186 abolishes aba responsiveness in the bt2 promoter even in the presence of abaresponsive region 186 to 43 this study provides novel insights into the regulatory mechanisms that underlie the synergistic regulation of starch synthesis and grain filling from sucrose and aba in cereal endosperm