Figure 7.

The collective roles of polarity determinants in ovule development comprise the balance model. (a) Expression summary of polarity determinants required for integument growth. During early ovule development CNA, PHB, and PHV (red), REV (all colored regions), ATS (blue), “?” unknown abaxial factor(s) which may share expression domain with ATS, and INO (green) mRNAs are specifically patterned along the chalaza. KAN1 and KAN2 (green) are predicted to be expressed in a similar fashion to INO. Once these patterns are established, persistent expression/action of all these transcription factors is required for proper integument growth. (b) The proposed polarity balance model. In the inner integument, ATS and the proposed additional abaxial factor (“?”) act in balanced opposition to CNA/PHB/PHV and REV to promote inner integument growth. Disruption of this balance by decrease or increase in either function alters the growth plane, leading to aberrant integument growth. Initiation of the inner integument precedes outer integument initiation in Arabidopsis, and thus growth of the outer integument is directly influenced by inner integument morphogenesis. In the outer integument, abaxial activities provided by INO, KAN1, and KAN2 act in balance with REV to control morphogenesis.