The systems and interactions underpinning complex cell wall patterning.

Cell walls can confer amazing properties to plant cells, particularly if they have complex patterns. Complex cell wall patterns in the primary cell wall often lead to complex cell shapes, whereas in the secondary cell wall they lead to advanced material properties that prepare cells for mechanically demanding tasks. Not surprisingly, many of these structures are found in water transporting tissues. In this review, I compare the mechanisms controlling primary and secondary cell wall patterns, with emphasis on water transporting tissues and insights derived from modeling studies. Much of what we know about this is based on complex cell shapes and primary xylem patterns, leading to an emphasis on the Rho-of-plants - cortical microtubule - cellulose microfibril system for secondary cell wall patterning. There is a striking diversity of secondary cell wall patterns with important functional benefits, however, about which we know much less and that may develop in substantially different ways.