Shared conserved module found in formation of moss midribs and axillary meristems of seed plants

The landing of plants is a major event during evolution. Accompanying their shift from aquatic to terrestrial habitats, different evolutionary plant lineages developed distinct characteristic body plans and anatomical structures, which gave plants the adaptive capacity to explore new environments.

Midribs are multilayered structures in the leaves of some mosses and are responsible for water conduction, as a beneficial complement to surface capillarity, while the axillary meristems (AM) of seed plants can form lateral branches as secondary growth axes instead of the terminal branch, which significantly altered plant architecture and affected fruit or seed production.

A research team from the University of Chinese Academy of Sciences (UCAS) and CAS Institute of Genetics and Developmental Biology discovered a shared molecular module between these two completely different anatomical structures.

In their study, Dr. WANG Ying and his colleagues revealed the mechanism underlying the organogenetic power of the LATERAL SUPPRESSOR gene in Arabidopsis and its orthologous genes in Physcomitrium patens.

By combining molecular genetics, confocal imaging and high-throughput transcriptome profiling to follow the formation processes of the two structures at cellular resolution, the researchers demonstrated that genes of the GRAS family promote the formation of non-homologous organs , the initiation of AD in Arabidopsis thaliana and the midrib. training at Physcomitrium patens.

They further showed that promotion of cell division is a common theme in two highly divergent species. Cell division is greatly impaired in Arabidopsis mutants, which explains the defects in AM formation.

Meanwhile, reduced cell division activity also leads to defects in midrib formation in mutant Physcomitrium leaves, the researchers said.

Their work provides a comparative analysis of the cellular processes underlying non-homologous organ formation and highlights a cryptic connection between the axillary meristem and water-conducting tissues in different lineages.

This study provides a striking example of a more universal mechanism associated with evolutionary innovation, i.e., a conserved regulatory module featuring the promotion of cell division was co-opted during evolution and reused in divergent development programs.

This work was supported by the National Natural Science Foundation of China, the National Key R&D Program of China, the Fundamental Research Funds for the Central Universities, and the Bureau of National Tobacco.

LAS genes regulate cell division in moss leaf midrib formation and AM angiosperm initiation. (Image by WANG Ying)

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