Abstract
The zygote is the first cell of a multicellular organism. In most angiosperms, the zygote divides asymmetrically to produce an embryo-precursor apical cell and a supporting basal cell. Zygotic division should properly segregate symbiotic organelles, because they cannot be synthesized de novo. In this study, we revealed the real-time dynamics of the principle source of ATP biogenesis, mitochondria, in Arabidopsis thaliana zygotes using live-cell observations and image quantifications. In the zygote, the mitochondria formed the extended structure associated with the longitudinal array of actin filaments (F-actins) and were polarly distributed along the apical-basal axis. The mitochondria were then temporally fragmented during zygotic division, and the resulting apical cells inherited mitochondria at higher concentration compared to the basal cells. Further observation of postembryonic organs showed that these mitochondrial behaviours are characteristic of the zygote. Overall, our results showed that the zygote has spatiotemporal regulation that unequally distributes the mitochondria.
Highlights
In most plant species, the multicellular body is generated from a unicellular zygote
In Arabidopsis thaliana, the apical–basal axis is already evident at the asymmetric division of the zygote, which generates one small apical cell and one large basal cell (Mansfield & Briarty, 1991). e apical cell actively proliferates to produce most of the embryonic organs, whereas the basal cell mostly yields the extra-embryonic suspensor (Gooh et al, 2015). is early embryogenesis would require massive energy production, because the principle source of ATP biogenesis, mitochondria, are necessary at this stage
Our findings show that the Arabidopsis zygote polarly distributes the mitochondria along the apical–basal axis, and concentrates the mitochondria into the embryo’s initial apical cell
Summary
The multicellular body is generated from a unicellular zygote. In Arabidopsis thaliana, the apical–basal (shoot–root) axis is already evident at the asymmetric division of the zygote, which generates one small apical cell and one large basal cell (Mansfield & Briarty, 1991). We used live-cell imaging of Arabidopsis zygotes and found that the vacuoles are polarly distributed in the zygote, causing their unequal inheritance into the basal daughter cell (Kimata et al, 2019). A er polar distribution along the apical–basal axis is completed, the filamentous mitochondria were temporally fragmented during zygotic division, segregated into the apical and basal daughter cells at different densities. Our findings show that the Arabidopsis zygote polarly distributes the mitochondria along the apical–basal axis, and concentrates the mitochondria into the embryo’s initial apical cell
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