Early division
Cells within organisms only divide when they have a certain amount of stem cell identity. Now Dutch researchers show in Development that the PLETHORA genes are turning on this stem cell identity directly after fertilisation.
To keep control over their shape, organisms tightly control which cells are allowed to divide. In general this will be the stem cells and the cells that directly derive from those. In plants these stem cells are located in the growth centres of the roots and shoots. Who when and where is allowed to divide is decided with help of a complex management system.
One group of genes that are controlling the dials of the management system are the PLETHORA genes. These determine how a cell divides. Longitudinal, perpendicular, or maybe diagonal. At the moment lots is known about how PLETHORA genes do their job in seedlings and older plants, but not so much in embryo’s.
To find out if PLETHORA genes are actual turned on in embryo’s the researchers firstly analysed if the genes that PLETHORA is regulating are also on during embryo development. De 197 genes that are controlled by PLETHORA turned out to be indeed turned on in developing embryo’s.
PLETHORA is needed right from the start to manage the cell divisions
Subsequently the researchers studied which PLETHORA gene is turned on when and where during embryo development. In total there are 6 PLETHORA genes. All 6, it turned out, are turned on at specific moments during embryo development. Each had its own pattern. Of the 6 two, PLETHORA 2 and 4 are already turned on shortly after fertilisation.
The researchers found out what the effect on the early embryo development PLETHORA 2 and 4 have. They did this by studying plants without PLETHORA 2 and 4, or to be more precise they studied plants in which one of the two genes was completely turned off, and the other reduced to half its original presence. They found that by about 25% of these plants embryo development stops shortly after fertilisation.
Studying the aborted embryo’s the researchers noticed that the majority of these embryo’s had not divided at all. By the aborted embryo’s that had divided, the division had not taken place at its expected place. PLETHORA is thus needed right from the start to manage the cell divisions.
Lastly the researchers asked if the other PLETHORA genes could replace PLETHORA 2 and 4 genes. This turned out to be the case. When they replaced PLETHORA 2 and 4 for PLETHORA 1 together with the instructions of being expressed like PLETHORA 2, then hardly any embryo’s aborted their development. This also shows that when and where PLETHORA genes are active determines it function more than the shape of its protein.
Literature
Merijn Kerstens, Carla Galinha, Hugo Hofhuis, Michael Nodine, Renan Pardal, Ben Scheres, Viola Willemsen; PLETHORA transcription factors promote early embryo development through induction of meristematic potential. Development 15 June 2024; 151 (12): dev202527. doi: https://doi.org/10.1242/dev.202527
Plant en Zo 