Heat-shock inducible clonal analysis reveals the stepwise establishment of cell fates in the rice stem

Katsutoshi Tsuda, Akiteru Maeno, and Ken-Ichi Nonomura

Plant Cell 2023 Sep 27 DOI:10.1093/plcell/koad241

Press release (In Japanese only)

The stem, composed of nodes and internodes, is the axis of shoots commonly seen among seed plants and is the most important target for regulating plant height in breeding practice. It is produced from the shoot apical meristem as a phytomer unit, along with the adjacent leaves and axillary buds. However, compared to other major organs such as leaves, roots, and flowers, our understanding of stem development has lagged far behind. Katsutoshi Tsuda, Akiteru Maeno, and Kenichi Nonomura at the National Institute of Genetics, Research Organization of Information and Systems, have defined the rice stem structure and described the developmental process using various approaches including micro CT. They also established a heat-shock inducible clonal analysis system and analyzed how cell fate establishment occurs for each organ during the development of the phytomer, which consists of the leaf, stem, and axillary bud. They found that cell fate establishment proceeds in a stepwise manner. First, cell fates for the phytomer are established prior to its initiation. Then, the emergence of cells that are destined for node splits of leaf and stem fates. Subsequently, the fate for the axillary bud fate is established. Finally, cell fate determination to the internodes occurs in a limited number of cells. This study clarified the key events and their chronological sequence in stem development, which had been unknown for a long time. It is expected to provide a basis for further research at the molecular level, which will lead to the improvement of stem traits for the design of ideal crops in the future.

Figure: The temporal order of cell fate acquisition in the rice stem. The fate of the flag leaf phytomer is established 10 to 5 days prior to its initiation. Fates for non-elongating domains such as foot II, node I, and the pulvinus start being established earlier than elongating domains. Internode II is the last part of the stem whose cell fate determination starts. It is likely to originate from a very limited number of cells between node I and foot II (inset). Black gradient lines at the bottom left show the start (left) and end (right) of cell fate establishment. Stages at which the founder cells are fully present are indicated by dots at the end of black lines.

Arita Group / Biological Networks Laboratory

Genome and transcriptome analyses reveal genes involved in the formation of fine ridges on petal epidermal cells in Hibiscus trionum

Shizuka Koshimizu*, Sachiko Masuda, Arisa Shibata, Takayoshi Ishii, Ken Shirasu, Atsushi Hoshino, Masanori Arita 
* Corresponding author

DNA Research 2023 Sep 11 DOI:10.1093/dnares/dsad019

Hibiscus trionum, commonly known as the ‘Flower of an Hour’, is an easily cultivated plant in the Malvaceae family, widespread in tropical and temperate regions, including drylands. The purple base part of its petal exhibits structural color due to the fine ridges on the epidermal cell surface, and the molecular mechanism of ridge formation has been actively investigated. We performed genome sequencing of H. trionum using a long-read sequencing technology with transcriptome and pathway analyses to identify candidate genes for fine structure formation. The ortholog of AtSHINE1, which is involved in the biosynthesis of cuticular wax in Arabidopsis thaliana, was significantly overexpressed in the iridescent tissue. In addition, orthologs of AtCUS2and AtCYP77A, which contribute to cutin synthesis, were also overexpressed. Our results provide important insights into the formation of fine ridges on epidermal cells in plants using H. trionum as a model.

This study was conducted by a collaborative research group comprising the National Institute of Genetics (Shizuka Koshimizu and Masanori Arita), RIKEN (Sachiko Masuda, Arisa Shibata, and Ken Shirasu), Arid Land Research Center, Tottori Univ. (Takayoshi Ishii), and National Institute for Basic Biology (Atsushi Hoshino).

This work was supported by JSPS KAKENHI grants to KS (20H05909), JST ACT-X grant to SK (JPMJAX21B6), a grant from Sapporo Bioscience Foundation to SK, and NIBB Collaborative Research Program to SK (20-341, 21-223, 22NIBB308, and 23NIBB314).

Reference
Moyroud, E., Wenzel, T., Middleton, R., et al. 2017, Disorder in convergent floral nanostructures enhances signalling to bees. Nature (2017) 550, 469–474.

Figure: H. trionum flower and comparison of the surface structures

On September 12, 2023, Mr. Harsha Somashekar (Plant Cytogenetics Laboratory, Nonomura Laboratory) received the Morishima Award from the Genetics Program, SOKENDAI. The Morishima Award is given to students in the Genetics Program to honor their outstanding performances during PhD studies and to encourage further achievements.

・Harsha Somashekar (Plant Cytogenetics Laboratory)
thesis title : GLUCAN SYNTHASE-LIKE5 promotes anther callose deposition to maintain timely initiation and progression of meiosis in rice (Oryza sativa L.)

▶ The Morishima Award

▶ — Professor Emeritus — MORISHIMA, Hiroko