High-temperature promotion of callus formation requires the BIN2-ARF-LBD axis in Arabidopsis.

The auxin-brassinosteroid interaction involving the BIN2-ARF-LBD axis plays a key role in temperature-dependent callus formation in Arabidopsis. An extensive web of multiple hormone signaling pathways underlies callus formation. Here, we report that a brassinosteroid (BR) signaling component, BR-INSENSITIVE 2 (BIN2), positively regulates callus formation. The BIN2 kinase promotes transcriptional activities of AUXIN RESPONSE FACTOR 7 (ARF7) and ARF19 and subsequently activates expression of LATERAL ORGAN BOUNDARIES-DOMAIN 16 (LBD16) and LBD29 during callus formation. Consistently, the BIN2 activity is dependent on ARFs in the control of callus formation. Notably, this auxin-BR interaction is particularly relevant in temperature-dependent callus formation. Misexpression of BIN2 and ARFs resulted in the temperature insensitivity of callus formation. These results indicate that the BIN2-ARF-LBD axis plays a key role in temperature-dependent callus formation in Arabidopsis.