RNAi of AGAMOUS genes in sweetgum alters reproductive organ identity and decreases fruit persistence

Abstract

Sweetgums (Liquidambar), members of the family Altingiaceae (Altingiales), have inflorescences and floral organs that are distinctive in structure compared with other angiosperms in which the roles of floral homeotic genes have been studied. To begin to understand the role of AGAMOUS (AG)-a floral homeotic gene that has a major role in stamen and carpel development-in development of the monosexual flowers of sweetgum, we used RNAi to reduce the expression of two members of the AG subfamily. Because AG suppression should induce floral sterility, RNAi might also provide a tool to mitigate the risks of invasiveness-and to reduce the production of its nuisance fruits or allergenic pollen-when sweetgum is used as an exotic shade or forest tree. We tested 33 independent transgenic events and non-transgenic controls during 10 years in the field. The RNAi-AG sweetgum trees maintained normal growth, phenology, and vivid fall coloration during the 10 years of study, but 8 insertion events had highly modified inflorescence and floral morphology. The modified flowers had anthers and carpels that were converted to flat leaf-like structures lacking pollen grains and ovules, respectively. The female inflorescences developed into dry papery structures that failed to produce seeds. These infructescences were smaller than control infructescences, and lost a greater percentage of biomass in a controlled decay assay. RNAi against AG genes was highly effective at impairing fertility and modifying reproductive development without significant vegetative effects in sweetgum and gave phenotypes distinct from, but similar to, that of AG loss of function in other angiosperms. K E Y W O R D S

Balancing Breeding for Growth and Fecundity in Radiata Pine (Pinus radiataD. Don) Breeding Programme

“…Indeed, major alleles were observed for fecundity related traits such as flowering time and floral meristem formation in trees (Bohlenius et al., 2006; Hsu et al., 2011; Tylewicz et al., 2015). AGAMOUS (AG) subgroup of MADS‐box genes and Leafy (LFY) genes are two examples (Klocko et al, 2020). For DBH, more numerous genes with small effects have been estimated in trees (Hall et al., 2016).…”

Variation in floral form of CRISPR knock-outs of the poplar homologs of LEAFY and AGAMOUS after FT heat-induced early flowering

“…As knowledge of the molecular biology of flowering has grown, methods that seek to suppress or eliminate the functions of key, highly conserved floral genes for genetic containment have grown. For example, RNAi directed against the floral genes LEAFY ( LFY ) and AGAMOUS ( AG ) have been at least partly successful in attenuating fertility in apple [ 3 ], sweetgum [ 4 ], and poplar [ 5–7 ]. Where the goal is complete disruption of gene function, CRISPR knockouts have become a powerful tool for genetic containment.…”