This is corn smut, a culinary valuable type of fungus. It starts life like a yeast sporidia by budding daughter cells until it finds a genetically suitable mating partner. Once it becomes dikaryotic it starts to form the fungal hypha and infects a single kernel forming what you see as a gall.
While deletirious, and often considered a blight by farmers, the immature galls can be sold for many times more than the corn if it had not been infected. They are called huitlacoche when being used as culinary, and are described as tasting sweet and savory with earthy tones.
When infecting the kernel, the corn tries to protect itself using a reactive oxygen species, that in turn is countered by the fungus's YAP1 gene that protects it from oxidative stress. Genetic research into M. Maydis has actually worked tangible results in our ongoing fight against breast cancer!
M. Maydis is a basidiomycota or "club type" fungus, which is to say it belongs to the same order as the classic mushrooms you're used to seeing such as fly aminita/agaric which is the inspiration for the Super Mario power up mushroom.
This fungus is also considered a model species as in it's sporidia phase is capable of accepting gene modification.
M. Maydis is also capable of synthesizing the essential amino acid lysine, which we need but cannot produce ourselves.
So, you see, not all corn infecting funguses are bad. Some are actually really cool, and have funny names like "smut".
