Calcium signalling mediates self-incompatibility response in the Brassicaceae

Area of Science:

• Plant reproductive biology
• Molecular genetics
• Cell signaling

Background:

• Self-incompatibility (SI) in Brassicaceae prevents self-fertilization.
• SI is controlled by S-locus genes encoding pollen ligand (SP11/SCR) and stigma receptor (SRK).
• The precise signaling pathway triggering SI remains largely unknown.

Purpose of the Study:

• To elucidate the signaling mechanism underlying self-incompatibility in Brassicaceae.
• To investigate the role of calcium ions (Ca2+) in the SI response.
• To identify the molecular players involved in Ca2+ influx during SI.

Main Methods:

• Utilized self-incompatible Arabidopsis thaliana expressing SP11/SCR and SRK.
• Measured cytoplasmic Ca2+ ([Ca2+]cyt) levels in stigma papilla cells.
• Employed pharmacological inhibitors (AP-5) and gene mutants (GLR) to assess signaling pathways.
• Observed effects of Ca2+ manipulation on pollen hydration and SI.

Main Results:

• Self-pollination specifically induced a significant increase in [Ca2+]cyt in papilla cells.
• SP11/SCR application triggered Ca2+ influx, inhibited by AP-5 (a glutamate receptor channel blocker).
• Artificial elevation of [Ca2+]cyt arrested wild-type pollen hydration.
• AP-5 treatment impaired SI, and Ca2+ increase was reduced in GLR mutants.

Conclusions:

• Calcium (Ca2+) influx into stigma papilla cells is essential for Brassicaceae self-incompatibility.
• Glutamate receptor-like (GLR) channels mediate Ca2+ influx, acting as a critical component of the SI signaling pathway.
• This Ca2+-dependent mechanism leads to the rejection of self-pollen.