Toyota will buy a 5.9% stake in Isuzu as part of a collaboration in engine technologies between the two companies.

The Japanese giant will buy 100 million Isuzu shares for an undisclosed sum.

Isuzu Motors had been allied with General Motors, but it sold its 7.9% stake in April. This deal highlights how Toyota is overtaking GM as the world’s biggest car manufacturer.

Toyota and Isuzu plan to work together in researching and developing small diesel engines, including cooperating on emission-control technologies as well as alternative fuel technologies.