(Sharecast News) - Citi upgraded its recommendation on Marks & Spencer shares to buy' from 'neutral' on Monday, as it argued that the investment case is "evolving"."Understanding the cultural change and the Ocado Retail JV is paramount to understand the rational for this pivot," it said.Back in February, M&S said it was buying a 50% share of Ocado's UK retail business for up to £750m. It said at the time that the JV would accelerate its food strategy as it enables the compay to take its food online in an "immediately profitable, scalable and sustainable way".Citi went on: "Accordingly we have undertaken a detailed bottom up scenario analysis of the Ocado Retail JV with Citi's Food Retail analyst Nick Coulter. We consider the aggregate of the structural changes has the potential to re-invigorate the M&S business to a greater degree than investors expect."It said the Ocado JV is an "elegant" solution to a structural gap in the M&S business model and reflects a bold decision to buy into a market leading online proposition."M&S is a business which is making itself more relevant for the next decade," Citi said, adding that its bottom-up scenario analysis suggests a possible £4.7bn sales base and £334m EBITDA after 15 years.Citi lifted its price target on M&S to 330p from 290p.