Stepwise cell fate establishment in the rice stem

Tsuda et al. investigate the temporal order of cell fate establishment during stem development in rice.

By Katsutoshi Tsuda

Background: The stem, which consists of nodes and internodes, is an axis of the shoot that physically supports lateral organs such as leaves and flowers and enables water transport and solute exchange. In contrast to other organs such as leaves, roots, and flowers, stem development remains poorly understood. In seed plants, the stem is produced from the shoot apical meristem as a part of the developmental unit called the phytomer, which comprises a leaf, a stem, and an axillary bud.

Question: In what temporal order is cell fate established for each organ in a phytomer? To address this question, we developed a heat shock-inducible clonal analysis system in rice (Oryza sativa). By introducing clonal sectors at various time points during flag leaf phytomer development, we examined whether the fate of a given cell is determined for a certain organ.

An immature stem of the flag leaf phytomer, consisting of node I, internode II, and foot II.

Findings: We found that cell fate establishment occurs stepwise for each organ. First, phytomer founder cells are determined before leaf initiation from the shoot apical meristem. Next, the fate of the node is determined in the meristem flank, splitting cell lineages destined for the leaf and the stem. Axillary bud cell fate is established shortly after leaf initiation. Finally, the cell population destined for internodes emerges from, at most, a few cell tiers in the stem. Therefore, the internode develops last in the phytomer.

Next steps: The molecular mechanisms governing early stem development are largely unknown. We demonstrated that there are distinct steps in phytomer development, and thus, the molecular features (e.g., gene expression) that characterize each step can now be determined experimentally. Developmental mutants with altered plant height can also provide insights into stem development.



Katsutoshi Tsuda, Akiteru Maeno and Ken-Ichi Nonomura. (2023). Heat-shock inducible clonal analysis reveals the stepwise establishment of cell fates in the rice stem.