There are a lot of land plants that already do very well during floods. For example in the US Southwest there are bands of land adjacent to rivers, the flood plains.
That is the habitat for several species of cottonwood trees. The life cycle of the trees depends on there being a yearly flood that lasts for weeks. In fact most of the native species on the flood plains there do very well during floods. Many require getting their "feet wet" for a month at a time to do well.
Damming rivers has stopped annual flooding during the Southwest monsoon season, so humans have had to intervene to maintain the cottonwood forests. How? Germinating seeds in water and then transplanting 3 year old cottonwood trees into the flood plain.
http://www.treenm.com/nm-tree-species/rio-grande-cottonwood/
So - no. Plants do not necessarily need aerenchyma tissues to survive flooding. So we do not need to go to the trouble of trying to migrate the genes.
In fact aquatic plants like you describe do poorly without having their "feet wet" most of the time.