# An XA21-Associated Kinase (OsSERK2) regulates immunity mediated by the XA21 and XA3 immune receptors

## TL;DR

This study shows that OsSERK2 is a key regulator of rice immune receptors XA21, XA3, and FLS2, enhancing immunity against bacterial leaf blight.

## Contribution

The paper identifies OsSERK2 as a novel positive regulator of multiple rice immune receptors through direct interaction and phosphorylation.

## Key findings

- OsSERK2 interacts with XA21, XA3, and FLS2 in a kinase-dependent manner.
- OsSERK2 forms a constitutive complex with XA21 in vivo and undergoes bidirectional trans-phosphorylation.
- Silencing OsSERK2 leads to altered plant morphology and reduced brassinolide sensitivity.

## Abstract

The rice XA21 immune receptor kinase and the structurally related XA3 receptor, confer immunity to Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial leaf blight. Here we report the isolation of OsSERK2 (rice somatic embryogenesis receptor kinase 2) and demonstrate that OsSERK2 positively regulates immunity mediated by XA21 and XA3 as well as the rice immune receptor FLS2 (OsFLS2). Rice plants silenced for OsSerk2 display altered morphology and reduced sensitivity to the hormone brassinolide. OsSERK2 interacts with the intracellular domains of each immune receptor in the yeast-two-hybrid system in a kinase activity dependent manner. OsSERK2 undergoes bidirectional trans-phosphorylation with XA21 in vitro and forms a constitutive complex with XA21 in vivo. Taken together, these results demonstrate an essential role for OsSERK2 in the function of three rice immune receptors and suggest that direct interaction with the rice immune receptors is critical for their function.