RNAi Suppression of LEAFY Gives Stable Floral Sterility, and Reduced Growth Rate and Leaf Size, in Field-Grown Poplars

The central floral development gene LEAFY (LFY), whose mutation leads to striking changes in flowering and often sterility, is commonly expressed in non-floral structures; however, its role in vegetative development is poorly understood. Sterility associated with suppression of LFY expression is an attractive means for mitigating gene flow by both seeds and pollen in vegetatively propagated forest trees, but the consequences of its suppression for tree form and wood production are unclear. To study the vegetative effects of RNAi suppression of LFY, we created a randomized, multiple-year field study with 30-40 trees (ramets) in each of two sterile gene insertion events, three transgenic control events, and a wild-type control population. We found that floral knock-down phenotypes were stable across years and propagation cycles, but that several leaf morphology and productivity traits were statistically and often substantially different in sterile vs. normal flowering RNAi-LFY trees. Though trees with suppressed LEAFY expression looked visibly normal, they appear to have reduced growth and altered leaf traits. LFY appears to have a significant role in vegetative meristem development, and evaluation of vegetative impacts from LFY suppression would be prudent prior to large-scale use for genetic containment.