Structural and transcriptional comparative analysis of the S locus regions in two self-incompatible Brassica napus lines

• Published in: The Plant cell Vol. 11; no. 11; pp. 2217 - 2231
• Main Authors: Cui, Y.H, Brugiere, N, Jackman, L, Bi, Y.M, Rothstein, S.J
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Physiologists 01.11.1999; American Society of Plant Biologists
• Subjects: Amino Acid Sequence; amino acid sequences; Animals; Base Sequence; Brassica - genetics; Brassica napus var. napus; Chromosome Mapping; Complementary DNA; Crosses, Genetic; DNA; DNA Transposable Elements; exons; gene expression; Genes; Genetic loci; Genome, Plant; Genomics; Glycoproteins - chemistry; Glycoproteins - genetics; Glycoproteins - metabolism; Haplotypes; introns; lines; loci; messenger RNA; Molecular Sequence Data; multiple genes; nucleotide sequences; Open Reading Frames; Plant cells; plant proteins; Plant Proteins - chemistry; Plant Proteins - genetics; Plant Proteins - metabolism; Pollen; Pollen - physiology; Polymerase chain reaction; Protein Kinases - genetics; Protein Kinases - metabolism; Retrotransposons; self incompatibility; Sequence Alignment; Sequence Homology, Amino Acid; Sequence Homology, Nucleic Acid; sll3 gene; transcription (genetics); Transcription, Genetic
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.11.11.2217

Self-incompatibility (SI) in Brassica is controlled by a single locus, termed the S locus. There is evidence that two of the S locus genes, SLG, which encodes a secreted glycoprotein, and SRK, which encodes a putative receptor kinase, are required for SI on the stigma side. The current model postulates that a pollen ligand recognizing the SLG/SRK receptors is encoded in the genomic region defined by the SLG and SRK genes. A fosmid contig of approximately 65 kb spanning the SLG-910 and SRK-910 genes was isolated from the Brassica napus W1 line. A new gene, SLL3, was identified using a novel approach combining cDNA subtraction and direct selection. This gene encodes a putative secreted small peptide and exists as multiple copies in the Brassica genome. Sequencing analysis of the 65-kb contig revealed seven additional genes and a transposon. None of these seven genes exhibited features expected of S genes on the pollen side. An approximately 88-kb contig of the A14S region also was isolated from the B. napus T2 line and sequenced. Comparison of the two S regions revealed that (1) the gene organization downstream of SLG in both S haplotypes is highly colinear; (2) the distance between SLG-A14 and SRK-A14 genes is much larger than that between SLG-910 and SRK-910, with the intervening region filled with retroelements and haplotype-specific genes; and (3) the gene organization downstream of SRK in the two haplotypes is divergent. These observations lead us to propose that the SLG downstream region might be one border of the S locus and that the accumulation of heteromorphic sequences, such as retroelements as well as haplotype-unique genes, may act as a mechanism to suppress recombination between SLG and SRK.