Ovule integument identity determination in Arabidopsis.

Ovules are the organs in which the female gametophyte develops. They develop in Arabidopsis and many other plant species from carpel tissue as new meristematic formations. In ovules we can distinguish three major parts which are the funiculus that attaches the ovule to the placenta, the integuments and the nucellus which contains the female gametophyte. Little is known about the molecular genetic regulatory cues that control the development of these ovule tissues. In the August issue of The Plant Cell, we have shown that there are genetic and molecular interactions between BELL1 and the MADS-box genes AGAMOUS, SEEDSTICK, SHATTERPROOF1 and SHATTERPROOF2 to control integument identity.1 We have shown that BEL1 directly interacts with a MADS-box dimer composed of AG and SEPALLATA3 and we proposed that this interaction is essential to prevent that integuments turn into carpels. Furthermore, we have shown that during ovule development BEL1 is important for the regulation of the stem cell maintenance gene WUSCHEL. In this Addendum we discuss addition literature data that sustain our model for integument development in Arabidopsis.