A small protein helps flowers to complete their development correctly

The flower clock!


How flowers form correctly within a limited time frame has been a mystery, at least until now. Scientists from the Nara Institute of Science and Technology and Nanjing University have solved this mystery. They discovered a multi-functional protein plays a significant role in ensuring the proper formation of the floral reproductive organ. This protein helps flowers to complete their development correctly and in a timely way.

During the early stages of flower development, stem cells provide the cell source for floral organ formation. In floral meristems, stem cell activities are maintained via a feedback loop between WUSCHEL (WUS), a gene that identifies floral stem cells, and CLAVATA3 (CLV3), a stem cell marker gene that is activated and sustained by WUS.

The repression of WUS by a protein called KNUCKLES (KNU) prompts the completion of floral stem cell activity correctly and in a timely way.

Erlei Shang, the lead author of the study, said, “What isn’t fully understood is how the robust floral stem cell activity finishes within a limited period to ensure carpel development.”

Senior author Toshiro Ito said, “The team’s research revealed that in Arabidopsis thaliana, KNU could completely deactivate the robust floral meristems at a particular floral stage.”

early stage flower of Arabidopsis thaliana
An early stage flower of Arabidopsis thaliana. Using confocal microscopy, Shang Erlei et al. found that KNUCKLES (KNU), encoding a C2H2-type zinc finger repressor, expresses in floral meristem (shown in red) from floral stage 6 and overlaps with the stem cell marker gene CLVTAVA3 (CLV3) expressing cells (shown in green). Further, KNU directly repressed CLV3 and mediates a regulatory framework for the timely controlled floral meristem determinacy. Credit: Bo Sun

KNU carries multiple functions via its position-specific roles. KNU both represses and silences WUS and directly represses CLV3 and CLV1 (a gene that encodes a receptor for the CLV3 peptide). As a result, KNU eliminates the CLV3-WUS feedback loop via transcriptional and epigenetic mechanisms. Also, the interaction of KNU with WUS protein disrupts the interactions required for the maintenance of floral meristems.

The corresponding author Bo Sun said, “Our results reveal a regulatory pathway where KNU plays a key role in supporting the completion of floral meristem development within a short time window and ensures that flower reproductive organs are properly formed.”

Scientists noted, “This research will be useful for genetic studies of food crops and global food production. The results of this research will be useful for genetic studies of food crop species such as rice, tomatoes, and maize.”

Journal Reference:
  1. Robust control of floral meristem determinacy by position-specific multifunctions of KNUCKLES, Proceedings of the National Academy of Sciences (2021). DOI: 10.1073/pnas.2102826118
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