Agriculture Reference
In-Depth Information
Figure 10.4
Model for the mechanism of sporophytic SI in Brassicaceae. Binding of SCR
1
to SRK
1
leads to derepression of SRK
1
by displacement of THL1. This leads to phosphorylation of both
effectors (ARC1 and possibly calmodulin) and negative regulators of SRK1 (KAPP and SNX1). The
dashed arrow represents unknown elements of the cascade, which ultimately lead to inhibition of pollen
germination and/or tube growth. Based on McCubbin and Kao (2000).
more than 100-fold more abundant than SRK in the stigma, this is a significant
consideration.
Akey question is how does this sequence of signalling events ultimately lead
to the inhibition of pollen germination or tube growth? ARC1 has been shown
to be both phosphorylated by SRK and essential for the SI response. As a U-box
containing protein ARC1 presumably targets various proteins for degradation - what
these might be is currently unknown. Calmodulin also interacts with the SRK kinase
domain and most likely serves to mediate cross-talk between calcium signalling in
pollination
per se
and SI signal transduction (Vanoosthuyse
et al.
, 2003). Exactly
