What is the relationship between the major agricultural regions in Japan and its political development?
I assume that you are asking about early Japanese development, in the Nara and Heian periods, for example. If so, attempts to control agricultural lands (and the failure of those attempts) was a major driver of Japanese political development.
Early in this time, Japanese elites were trying to recreate the Chinese system, complete with a centralized government in Nara. These elites tried to take control of agricultural lands. Their success was fleeting because they really did not have enough strength to control those areas. This led to a breakdown of the attempts at centralized government and a move towards feudalism. The move towards feudalism occurred as local elites were able to keep control of agricultural lands in their areas and eventually had to be treated as feudal lords. This led to a political system in Japan that was feudal in nature.