Cell remodeling and subtilase gene expression in the actinorhizal plant Discaria trinervis highlight host orchestration of intercellular Frankia colonization

FOURNIER J; IMANISHI L; CHABAUD M; ABDOU-PAVY I; GENRE A; BRICHET L; LASCANO R; MUÑOZ N; VAYSSIÈRES A; PIRROLLES E; BROTTIER L; GHERBI H; HOCHER V; SVISTOONOFF S; BARKER DG; WALL LG

NEW PHYTOLOGIST

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2018 vol. 219 p. 1018 - 1030

0028-646X

Nitrogen-fixing filamentous Frankia colonize the root tissues of its actinorhizal host Discaria trinervis via an exclusively intercellular pathway. Here we present studies aimed at uncovering the mechanisms associated with this little-researched mode of root entry, and in particular the extent to which the host plant is an active partner during this process. The detailed characterization of the expression patterns of infection-associated host genes has provided valuable tools to identify intercellular infection sites, thus allowing in vivo confocal microscopic studies of the initial stages of Frankia colonization of the D. trinervis root. The subtilisin-like serine protease gene Dt12, as well as its Casuarina glauca homologue Cg12, are specifically expressed at sites of Frankia intercellular entry of the D. trinervis root. This colonization is systematically associated with both nucleo-cytoplasmic reorganisation in adjacent host cells and a major remodeling of the intercellular apoplastic compartment. These results lead to the proposition that the actinorhizal host root modifies both the size and composition of the intercellular apoplast in order to accommodate the filamentous microsymbiont. The implications of these findings are discussed, including the possible analogies that can be drawn with the well-studied orchestrating role of the host legume during intracellular root hair colonization by nitrogen-fixing rhizobia.