Browsing by Author "Howe, Glenn T."

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    Overexpression of SHORT VEGETATIVE PHASE-LIKE (SVL) in Populus delays onset and reduces abundance of flowering in field-grown trees
    Goralogia, Greg S.; Howe, Glenn T.; Brunner, Amy M.; Helliwell, Emily; Nagle, Michael F.; Ma, Cathleen; Lu, Haiwei; Goddard, Amanda L.; Magnuson, Anna C.; Klocko, Amy L.; Strauss, Steven H. (2021-12)
    The spread of transgenes and exotic germplasm from planted crops into wild or feral species is a difficult problem for public and regulatory acceptance of genetically engineered plants, particularly for wind-pollinated trees such as poplar. We report that overexpression of a poplar homolog of the floral repressor SHORT VEGETATIVE PHASE-LIKE (SVL), a homolog of the Arabidopsis MADS-box repressor SHORT VEGETATIVE PHASE (SVP), delayed the onset of flowering several years in three genotypes of field-grown transgenic poplars. Higher expression of SVL correlated with a delay in flowering onset and lower floral abundance, and did not cause morphologically obvious or statistically significant effects on leaf characteristics, tree form, or stem volume. Overexpression effects on reproductive and vegetative phenology in spring was modest and genotype-specific. Our results suggest that use of SVL and related floral repressors can be useful tools to enable a high level of containment for vegetatively propagated short-rotation woody energy or pulp crops.
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    RNA interference suppression of AGAMOUS and SEEDSTICK alters floral organ identity and impairs floral organ determinacy, ovule differentiation, and seed-hair development in Populus
    Lu, Haiwei; Klocko, Amy L.; Brunner, Amy M.; Ma, Cathleen; Magnuson, Anna C.; Howe, Glenn T.; An, Xinmin; Strauss, Steven H. (2019-04)
    The role of the floral homeotic gene AGAMOUS (AG) and its close homologues in development of anemophilous, unisexual catkins has not previously been studied. We transformed two RNA interference (RNAi) constructs, PTG and its matrix-attachment-region flanked version MPG, into the early-flowering female poplar clone 6K10 (Populus alba) to suppress the expression of its two duplicate AG orthologues. By early 2018, six out of 22 flowering PTG events and 11 out of 12 flowering MPG events showed modified floral phenotypes in a field trial in Oregon, USA. Flowers in catkins from modified events had carpel-inside-carpel' phenotypes. Complete disruption of seed production was observed in seven events, and sterile anther-like organs in 10 events. Events with strong co-suppression of both the two AG and two SEEDSTICK (STK) paralogues lacked both seeds and associated seed hairs. Alterations in all of the modified floral phenotypes were stable over 4yr of study. Trees from floral-modified events did not differ significantly (P<0.05) from nonmodified transgenic or nontransgenic controls in biomass growth or leaf morphology. AG and STK genes show strong conservation of gene function during poplar catkin development and are promising targets for genetic containment of exotic or genetically engineered trees.