Seed development in angiosperms demands the tightly coordinated development of three genetically distinct structures. The embryo is surrounded by the endosperm, which is in turn enclosed within the maternally derived seed coat. In Arabidopsis, final seed size is determined by early expansion of the coenocytic endosperm, which then cellularises and subsequently undergoes developmental programmed cell death, breaking down as the embryo grows. Endosperm breakdown requires the endosperm-specific basic helix-loop-helix transcription factor ZHOUPI. However, to date, the mechanism underlying the Arabidopsis endosperm breakdown process has not been elucidated. Here, we provide evidence that ZHOUPI does not induce the developmental programmed cell death of the endosperm directly. Instead ZHOUPI indirectly triggers cell death by regulating the expression of cell wall-modifying enzymes, thus altering the physical properties of the endosperm to condition a mechanical environment permitting the compression of the cellularised endosperm by the developing embryo.
The authors declare no competing or financial interests.
L.B., C.F., S.C. and A.C. carried out experiments, analysed results and prepared figures. All authors participated in experimental design and manuscript preparation. G.I. planned and directed the project.
This work was funded by a fellowship from AgreenSkills (CESETAB project) and Institut National de la Recherche Agronomique (to C.F.); a ‘Chaire d'excellence’ from l’Agence Nationale de la Recherche, France [ANR-10-CHEX-0011: mécanograine to G.I.]; and a European Research Council Starting Grant [Phymorph #307387 to A.B.].
Supplementary information available online at http://dev.biologists.org/lookup/doi/10.1242/dev.137224.supplemental
- Received March 7, 2016.
- Accepted May 24, 2016.