BAM3 Is a CLE19 Receptor that Mediates a Distinct Signaling Branch Controlling Tapetum Degeneration and Pollen Wall...

Area of Science:

• Plant reproductive biology
• Molecular plant science
• Cell signaling

Background:

• Pollen wall formation is crucial for plant reproduction, requiring precise regulation of tapetum development and function.
• The peptide CLE19 in Arabidopsis is known to restrict tapetal activity, but its signaling specificity and robustness mechanisms are not fully understood.

Purpose of the Study:

• To identify additional receptors for the CLE19 peptide and elucidate their role in regulating tapetum differentiation and pollen wall formation.
• To understand how CLE19 signaling achieves developmental specificity and robustness through a dual-receptor system.

Main Methods:

• Genetic analysis of Arabidopsis mutants.
• Cytological and biochemical assays.
• Transcriptomic profiling (RNA sequencing).
• AlphaFold3 modeling and structure-guided mutagenesis.

Main Results:

• BARELY ANY MERISTEM 3 (BAM3) was identified as a novel receptor for CLE19.
• Disruption of BAM3 signaling led to impaired tapetum differentiation, disrupted secretory homeostasis, and abnormal pollen exine patterning.
• BAM3 mediates distinct CLE19-responsive genes, including pathways for tapetal degeneration, exine biosynthesis, flavonoid metabolism, and pollen wall development.
• CLE19-dependent assembly of a BAM3-SERK1/2 receptor complex was biochemically supported, revealing a distinct perception module.

Conclusions:

• A dual-receptor architecture for CLE19 signaling, involving BAM3 and PXL1, ensures robust male reproductive development.
• BAM3 mediates a transcriptionally distinct branch of CLE19 signaling, complementing the PXL1 pathway.
• Combinatorial peptide-receptor usage expands signaling capacity, coordinating complex developmental processes like pollen wall formation.