75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

227 LEAFY and the Evolution of Rosette Flowering in Idahoa
Michael White, Nicole Van Abel, Marek Sliwinski, David Baum
University of Wisconsin
The Brassicaceae species Idahoa scapigera (Isc) produces all of its flowers on long pedicels that derive from the
axils of rosette leaves (rosette flowering). Unlike most species of Brassicaceae, Idahoa has two, divergent LEAFY
(LFY) paralogs. Previous work showed that IscLFY1 driven by its native cis-regulatory regions could be introduced
into an Arabdiopsis lfy mutant background and could completely rescue stamen and carpel defects; however, IscLFY1
transgenic lines were deficient in petal production and showed architectural defects including internode compression
and the production of bracteate flowers. Here, we conducted the equivalent experiment with IscLFY2 and found full
rescue of LFY-dependent floral traits. IscLFY2 transgenic lines did not show detectable internode compression or bract
production, but a significant proportion of the lines produced terminal flowers. When introduced into an IscLFY1;lfy
genetic background, IscLFY2 rescued the architectural and petal-loss defects, but also yields many lines with terminal
flowers. Examination of the IscLFY2 cis-regulatory region reveals greater similarity to the equivalent region of LFY
than was true for IscLFY1, which may explain the more complete rescue of the lfy mutation. Fusion of the IscLFY2 5’
cis-regulatory region to a GUS reporter gene yielded relatively normal expression in all floral whorls, but additional
expression in the inflorescence meristem (IM), which can explain the production of terminal flowers. This result is similar
to that found with the LFY homolog from another rosette flower species, Leavenworthia crassa (Lcr). It is plausible
that terminal flower production by IscLFY2 and LcrLFY is indicative of a similar change in LFY regulation in these
two lineages and opens up the possibility that this regulatory change may have contributed to these parallel origins of
rosette flowering. The fact that IscLFY1 shows only incomplete rescue suggests that this paralog is either only partially
functional (perhaps en route to non-functionalization) or that the two LFY genes of Idahoa have been subfunctionalized,
with IscLFY1 playing a role that is not detectable in an Arabidopsis genetic background.
228 Cytoplasmically Localized CRY1 Promotes Blue-light-dependent Cotyledon Expansion in
Arabidopsis
Guosheng Wu, Tessa Durham, Edgar Spalding
Department of Botany, University of Wisconsin, Madison, Wisconsin
Cryptochromes are blue light receptors that mediate many aspects of plant photomorphogenesis, including inhibition
of hypocotyl elongation and promotion of cotyledon expansion in seedlings. Null cry1 mutants develop long hypocotyls,
long petioles, and smaller cotyledon blades compared to wild type when grown in blue light. Studies have shown that CRY1
is located both in the nucleus and the cytoplasm. To compare the contributions to seedling development of cytoplasmic
and nuclear CRY1, we generated transgenic cry1 plants expressing GFP-CRY1 with a nuclear localization signal (35S::
GFP-NLS-CRY1) or a nuclear export signal (35S::GFP-NES-CRY1) and compared their phenotypes with 35S::GFP-CRY1
plants. Confocal analysis of plants overexpressing GFP-NLS-CRY1 and GFP-CRY1 showed a strong concentration of
CRY1 in the nucleus. The long hypocotyl and petiole phenotypes of cry1 seedlings grown in blue light were strongly
rescued by these constructs. However, the smaller cotyledon area of cry1 was not rescued. Confocal analysis of plants
expressing GFP-NES-CRY1 showed that CRY1 was located in the cytoplasm in high blue light. Cotyledon growth in
these lines was rescued, being promoted even beyond wild-type size. This indicates that in blue light, cytoplasmic CRY1
promotes cotyledon expansion. The hypocotyl and petiole phenotypes were only partially rescued. Either cytoplasmic
CRY1 has some influence on these processes or an undetectable trace amount of nuclear CRY1 was responsible for this
partial rescue.