The receptor-like kinases BAM1 and BAM2 are required for root xylem patterning

Area of Science:

• Plant biology
• Molecular genetics
• Developmental biology

Background:

• Xylem patterning in plant roots relies on gradients of microRNAs (miRNAs) and their targets, HD-ZIP III transcription factors.
• The cell-to-cell movement of miR165/6 through plasmodesmata is crucial for xylem development, but its regulation is not fully understood.

Purpose of the Study:

• To investigate the role of receptor-like kinases (RLKs) in regulating the trafficking of miR165/6 and its impact on xylem patterning.
• To identify the specific RLKs involved in controlling the distribution of HD-ZIP III transcripts.

Main Methods:

• Simultaneous mutation of plasma membrane- and plasmodesmata-localized RLKs, BARELY ANY MERISTEM (BAM) 1 and 2.
• Expression of the geminivirus-encoded BAM1/2-interactor C4.
• Analysis of HD-ZIP III transcript accumulation and distribution.
• Assessment of root xylem patterning defects in Arabidopsis.

Main Results:

• Simultaneous mutation of BAM1 and BAM2, or expression of C4, led to increased accumulation and broader distribution of HD-ZIP III transcripts.
• Total miR165/6 accumulation remained normal, indicating a specific effect on target transcript distribution.
• These changes resulted in significant defects in root xylem patterning.
• BAM1 and BAM2 function redundantly in ensuring proper distribution of miR165/6-targeted transcripts.

Conclusions:

• BARELY ANY MERISTEM (BAM) 1 and 2 are redundantly required for correct xylem patterning in Arabidopsis roots.
• BAM1 and BAM2 regulate xylem patterning by controlling the distribution and accumulation of miR165/6-targeted transcripts.
• These findings elucidate a novel mechanism for miRNA-mediated developmental patterning in plants.