Structural basis for specific self-incompatibility response in Brassica.
Self-incompatibility (SI) is a widespread mechanism in flowering plants which prevents self-fertilization and inbreeding. In Brassica, recognition of the highly polymorphic S-locus cysteine-rich protein (SCR; or S-locus protein 11) by the similarly polymorphic S-locus receptor kinase (SRK) dictates the SI specificity. Here, we report the crystal structure of the extracellular domain of SRK9 (eSRK9) in complex with SCR9 from Brassica rapa. SCR9 binding induces eSRK9 homodimerization, forming a 2:2 eSRK:SCR heterotetramer with a shape like the letter "A". Specific recognition of SCR9 is mediated through three hyper-variable (hv) regions of eSRK9. Each SCR9 simultaneously interacts with hvI and one-half of hvII from one eSRK9 monomer and the other half of hvII from the second eSRK9 monomer, playing a major role in mediating SRK9 homodimerization without involving interaction between the two SCR9 molecules. Single mutations of residues critical for the eSRK9-SCR9 interaction disrupt their binding in vitro. Our study rationalizes a body of data on specific recognition of SCR by SRK and provides a structural template for understanding the co-evolution between SRK and SCR.
Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Rui
R
Ma
Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Zhifu
Z
Han
Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Zehan
Z
Hu
Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Guangzhong
G
Lin
Institute for Mathematical Sciences, Renmin University of China, 100872.
Xinqi
X
Gong
Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Heqiao
H
Zhang
Section of Plant Biology, 412 Mann Library Building, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853, USA.
June B
JB
Nasrallah
Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
Jijie
J
Chai
D000595:Amino Acid Sequence; D001937:Brassica / Q000378:metabolism*; D018360:Crystallography, X-Ray; D019281:Dimerization; D016296:Mutagenesis; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
D010940:Plant Proteins; D011494:Protein Kinases; C079832:S-receptor kinase