AUTHOR=Ma Lisong , Borhan M. Hossein 

TITLE=The receptor-like kinase SOBIR1 interacts with Brassica napus LepR3 and is required for Leptosphaeria maculans AvrLm1-triggered immunity

JOURNAL=Frontiers in Plant Science

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.00933

DOI=10.3389/fpls.2015.00933

ISSN=1664-462X

ABSTRACT=<p>The fungus <italic>Leptosphaeria maculans</italic> (<italic>L. maculans</italic>) is the causal agent of blackleg disease of canola/oilseed rape (<italic>Brassica napus</italic>) worldwide. We previously reported cloning of the <italic>B. napus</italic> blackleg resistance gene, <italic>LepR3</italic>, which encodes a receptor-like protein. LepR3 triggers localized cell death upon recognition of its cognate Avr protein, AvrLm1. Here, we exploited the <italic>Nicotiana benthamiana</italic> model plant to investigate the recognition mechanism of AvrLm1 by LepR3. Co-expression of the <italic>LepR3/AvrLm1</italic> gene pair in <italic>N. benthamiana</italic> resulted in development of a hypersensitive response (HR). However, a truncated <italic>AvrLm1</italic> lacking its indigenous signal peptide was compromised in its ability to induce <italic>LepR3</italic>-mediated HR, indicating that AvrLm1 is perceived by LepR3 extracellularly. Structure-function analysis of the AvrLm1 protein revealed that the C-terminal region of AvrLm1 was required for <italic>LepR3</italic>-mediated HR in <italic>N. benthamiana</italic> and for resistance to <italic>L. maculans</italic> in <italic>B. napus</italic>. LepR3 was shown to be physically interacting with the <italic>B. napus</italic> receptor like kinase, SOBIR1 (BnSOBIR1). Silencing of <italic>NbSOBIR1</italic> or <italic>NbSERK3 (BAK1)</italic> compromised LepR3-AvrLm1-dependent HR in <italic>N. benthamiana</italic>, suggesting that <italic>LepR3</italic>-mediated resistance to <italic>L. maculans</italic> in <italic>B. napus</italic> requires <italic>SOBIR1</italic> and <italic>BAK1/SERK3</italic>. Using this model system, we determined that BnSOBIR1 and SERK3/BAK1 are essential partners in the LepR3 signaling complex and were able to define the AvrLm1 effector domain.</p>