Synthesis and degradation of fructose 2,6-bisphosphate. Regulates carbon partitioning between sucrose versus starch during the diurnal cycle. beta-D-fructose 2,6-bisphosphate + H2O = beta-D-fructose 6-phosphate + phosphate ATP + beta-D-fructose 6-phosphate = ADP + beta-D-fructose 2,6-bisphosphate + H(+) 6-phosphofructo-2-kinase activity is activated by pyruvate. 6-phosphofructo-2-kinase activity is inhibited by PPi, phosphoenolpyruvate and 2-phosphoglycerate. Fructose-2,6-bisphosphatase activity is inhibited by pyruvate, fructose 1,6-bisphosphate and 6-phosphogluconate. Inactivated by mild heat treatment (42 degrees Celsius during 10 minutes). Interacts with 14-3-3 proteins; these interactions may regulate both nitrate assimilation and sucrose/starch partitioning in leaves during the diurnal cycle. Phosphorylation at Ser-220 and Ser-303 by CPK3 promotes 14-3-3 proteins binding. In the C-terminal section; belongs to the phosphoglycerate mutase family.