Scattering
Scattering or non-scattering of seeds is on of the differences between wild and domesticated plants. Non-scattering makes harvesting crops a lot easier. Not surprising researchers like to know the workings of this scattering process. As well as its responsible genes. For grasses, like wheat and rice, lots is known about the mechanical aspects of scattering. But now American researchers discovered the gene needed to initiate this mechanic.
To enable future scattering, plant build in breaking points. Locations that are less supported and easily break. They are at the end of the stele of a leaf, but also there where a seed is attached to the plant.
Making these locations less supportive occurs through giving the cell walls of the cells on these locations more lignin. As long as these cells are alive, all is well. But as soon as they die, they shrink and break their connections with neighbouring cells. But what this dying initiates is difficult to analyse, the genes that regulate the amount of lignin in the cell walls and initiate this dying appear to overlap. To overcome this difficulty, the researchers used green foxtail, a grass whose breaking points do not have extra lignin.
Earlier research gave the researchers the hint that SH1, for SHATTERING1, is involved in the scattering of seeds. To check this the researchers created green foxtail plants without SH1. While green foxtail plants with SH1 let go of their seeds, plant without any SH1 kept a strong hold on them. The researchers studied the amount of lignin at the breaking points of plants with and without SH1. Here they noticed no difference. SH1-lacking plants are not keeping hold of their seeds due to a reduced amount of lignin.
SH1 influences auxin dynamics of breaking point cells
To discover how SH1 initiates the scattering of seeds the researchers carefully studied the plants in the days leading up to the scattering. They observed that by plants with SH1 their breaking points slowly turn from green to yellow. This was not the case in SH1-lacking plants. This colour shift turned out to be a result of a reduction of chlorophyl, a sign that the cells were dying.
Because the researchers knew that plant hormones can have a role in the scattering process, they studied the effect of these hormones in plants that do have SH1. Observing that when applying auxin at the breaking point plants with SH1 keep their seeds longer. Zooming in at SH1-lacking breaking point cells, the researchers observed that the location of auxin in these cells was of importance. They noticed that in SH1-lacking cells auxin was located more often at the chlorophyl.
To confirm that SH1 is influencing auxin, the researchers analysed the difference in gene expression of breaking point cells with and without SH1. Noticing that a lot of auxin related genes had a different expression in SH1-lacking breaking point cells that in breaking point cells with SH1.
It appears that SH1 indeed influences the auxin dynamics of breaking point cells. How SH1 does this is not completely clear. To clarify this more research is needed, the researchers say. But this study shows that SH1 with help of auxin initiates the breaking point mechanics.
Literature
Yu, Y., Hu, H., Voytas, D.F., Doust, A.N. and Kellogg, E.A. (2023), The YABBY gene SHATTERING1 controls activation rather than patterning of the abscission zone in Setaria viridis. New Phytol. https://doi.org/10.1111/nph.19157
Plant en Zo 