The MD1000 is only officially supported with the PERC5E or PERC6E. Neither of those is officially supported with a PowerEdge R720.
So your only options will be non-supported solutions.
You can either get a PERC H810 and a non-Dell cable to hook the MD1000 (SFF-8470 connector) to the H810 (SFF-8088 connector), or you get a PERC6E and try it in the R720. Most likely the PERC6E will work just fine, but I personally have not tried it, so I cannot say 100% for sure.