Biology Reference
In-Depth Information
Conclusions
We have shown that DUO1 is both necessary and sufficient for the expression of
several male germline genes including AtGCS1 that is required for gamete fusion
[13], thus DUO1 has a major role in the specification of functional male gametes.
DUO1 is not involved in regulating microspore division and is first expressed in
germ cells after asymmetric division. DUO1 is also required for the entry of male
germ cells into mitosis and for the germline expression of the G2/M regulator
AtCycB1;1. Thus, the germ cell programme under DUO1 control has an impor-
tant role in regulating core cell cycle machinery specifically in the male germline.
The discovery of the dual role of DUO1 as a positive regulator in male germline
specification and cell cycle progression is a major advance in uncovering the mo-
lecular mechanisms involved in plant sexual reproduction. DUO1 is currently the
only regulatory factor that has been shown to be required for gamete specification
in plants. Recently we described an independent mechanism for male germ cell
cycle regulation where the F-BOX protein FBL17 controls germ cell entry into
S-phase via the degradation of the CDKA inhibitors KRP6 and 7 [4]. Taken to-
gether these data establish a molecular framework for twin sperm cell production
in flowering plants (Figure 5).
Figure 5.
Regulatory events in plant male germ cell production and specification.
Model integrating
the role of DUO1 and SCFFBL17 [18] in plant germ cell production and specification. The
germline-specific DUO1 protein (blue) activates the expression of several germline specific proteins (red). In
parallel, the CDKA inhibitors KRP6 and KRP7 (green) are expressed in the vegetative cell and germ cell after
asymmetric division, where they inhibit CDKA activity and S phase progression. The F-box protein FBL17
is then transiently expressed in the germline and forms an SCFFBL17 complex (blue) that targets KRP6/7
for proteasome dependent proteolysis, licensing S-phase progression (green arrow). Further germ cell cycle
progression is controlled by the DUO1-dependent G2/M phase expression of the CDKA regulatory subunit
AtCYCB1;1 (red). Thus, while SCFFBL17 and DUO1 promote male germ cell proliferation at successive stages
of the cell cycle, DUO1 integrates germ cell specification and division to ensure the production of functional
twin sperm cells that are essential for double fertilization. Arrows indicate a requirement for the protein rather
than direct binding.
