Embryo sac development relies on symplastic signals from ovular integuments in Arabidopsis.

SUMMARY: Ovules are female reproductive organs of angiosperms, consisting of sporophytic integuments surrounding female gametophytes, that is, embryo sacs. Synchronization between integument growth and embryo sac development requires intracellular communication. However, signaling routes through which cells of the two generations communicate are unclear. We report that symplastic signals through plasmodesmata (PDs) of integuments are critical for the development of female gametophytes. Genetic interferences of PD biogenesis either by functional loss of CHOLINE TRANSPORTER‐LIKE1 (CTL1) or by integument‐specific expression of a mutated CALLOSE SYNTHASE 3 (cals3m) compromised PD formation in integuments and reduced fertility. Close examination of pINO:cals3m or ctl1 ovules indicated that female gametophytic development was either arrested at various stages after the formation of functional megaspores. In both cases, defective ovules could not attract pollen tubes, leading to the failure of fertilization. Results presented here demonstrate a key role of the symplastic route in sporophytic control of female gametophytic development. Significance Statement: By examining a mutant defective in plasmadesmata (PDs) formation and by genetically interfering with PD formation specifically in integuments, this study demonstrates a key role of PD in integument‐mediated female gametophytic development, implying the involvement of syplasmic transport in this process. [ABSTRACT FROM AUTHOR]