Twenty years of research on cerato-platanin family proteins: clues, conclusions, and unsolved issues

Twenty years of research on cerato-platanin family proteins (CPPs) have led to some clearconclusions: CPPs are exclusively present in the fungal kingdom and possess anoutstanding capacity to stimulate the immune system of plants. Recent discoveries havehighlighted remarkable structural and functional similarities between CPPs and expansins,a class of non-enzymatic proteins found in both plants and microbes possessing looseningability on the cell wall structure. Nevertheless, the determination of a biological role forCPPs in fungi is becoming a complicated puzzle to solve, since experimental data are oftendivergent and point to functional diversification. A general consensus appears howeverpossible: CPPs from pathogenic and beneficial fungi may be considered as microbeassociatedmolecular patterns (MAMPs) and likely play a dual role, exerting functions inthe fungal cell wall and/or in plant colonization. In this review, which celebrates 20 y ofresearch on CPPs, we trace the history of these proteins and highlight experimental evidenceand still unsolved issues.