Control of stem cell niche and fruit development in Arabidopsis thaliana by AGO10/ZWL requires the bHLH transcription factor INDEHISCENT

Background: The shoot apical meristem (SAM) in plants is composed of a small mound of pluripotent stem cells that generate new organs. ARGONAUTE10 (AGO10) is known to be critical for maintenance of the embryonic SAM by regulating the expression of Class III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) transcription factors, which then modulate downstream responses to the key phytohormone auxin. However, we do not understand how AGO10 modulates auxin responses after embryogenesis in the mature plant. Results: Here we show that AGO10 regulates auxin responses in the post-embryonic SAM via the bHLH transcription factor INDEHISCENT (IND). IND directly regulates auxin responses in the SAM regulating the auxin transporter PIN1 via direct transcriptional regulation of PINOID kinase. We show that a loss of function ind mutation significantly restores ago10zwl-3 mutant SAM and fruit phenotypes. ago10zwl-3 mutants overexpress IND and overexpression of IND phenocopies the ago10zwl-3 SAM phenotypes, and regulates auxin transport and responses in the SAM. AGO10 also regulates post-embryonic development in the fruit via a similar genetic pathway. Conclusions: We characterise a molecular mechanism that is conserved during post embryonic development linking AGO10 directly to auxin responses.