Ethylene and ripening-regulated expression and function of fruit cell wall modifying proteins

Two decades of research have provided deep insights into the regulation of cell wall disassembly in ripening fruit. These insights have been important in understanding ethylene-regulated processes of fruit softening in climacteric fruit but have also provided insights into non-climacteric fruit softening as well as cell wall disassembly that accompanies many plant developmental processes such as cell growth and abscission. Major results indicate that no single gene or enzyme can account for the major events that underlie fruit softening and that many of the potentially responsible genes and their corresponding cell wall modifying proteins are members of large gene families that exhibit overlapping patterns of expression and possibly redundant biochemical action. The cooperative action of cell wall modifying proteins and enzymes has been demonstrated to participate in fruit softening as well as to the ripening-regulated increase in necrotrophic pathogen susceptibility. A general model of cooperative cell wall disassembly is now firmly established and future research focusing on complex interactions between cell wall modifying proteins and enzymes and between the major cell wall matrices should be productive in elucidating a general model of ripening-regulated cell wall disassembly and fruit softening.