Regulatory subunit of pyrophosphate--fructose 6-phosphate 1-phosphotransferase. Allosterically activated by fructose 2,6-bisphosphate. Carbohydrate degradation; glycolysis; D-glyceraldehyde 3-phosphate and glycerone phosphate from D-glucose: step 3/4. Tetramer of two alpha (regulatory) and two beta (catalytic) chains. Expressed in roots and specific parts such as the trichomes of leaves, cotyledon veins, as well as in stamen and gynoecium of flowers. Belongs to the phosphofructokinase type A (PFKA) family. PPi-dependent PFK group II subfamily. Clade 'Long' sub-subfamily.