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Many flowering plants possess a self-incompatibility system to prevent inbreeding. In Brassica rapa, self/ non-self recognition in mating is established through S-haplotype-specific interactions between stigma receptors and S-locus protein 11 (SP11, also called S-locus cysteine-rich protein) that is encoded at the highly polymorphic S-locus. Here we describe the solution structure of the SP11 protein of the S 8 -haplotype (S 8 -SP11), which specifically binds to the stigma factor of the same haplotype. It folds into an ␣/␤ sandwich structure that resembles those of plant defensins. Residues important for structural integrity are highly conserved among the allelic SP11s, suggesting the existence of a common folding pattern. Structure-based sequence alignment and homology modeling of allelic SP11 identified a hypervariable (HV) region, which is thought to form a loop that bulges out from the body of the protein that is amenable to solvent exposure. We suggest that the HV region could serve as a specific binding site for the stigma receptor. Self-incompatibility (SI)1 is one of several mechanisms available to flowering plants to prevent inbreeding and thereby promote out-crossing (1). SI is based on self and non-self discrimination processes between pollens and stigmas, followed by selective inhibition of self pollen germination and/or growth. For Brassica rapa, the SI system is controlled sporophytically by multiple haplotypes at a single locus, termed the S-locus. Recognition between pollen and stigma is achieved by gene products of the S-locus, which contains three highly polymorphic genes: SP11/SCR (2, 3), S-locus receptor kinase (SRK) (4), and S-locus glycoprotein (SLG) (5, 6). SP11 encodes a small cysteine-rich protein that determines the S-haplotype specificity of pollen, whereas SRK encodes a transmembrane receptorlike serine-threonine kinase that determines the S-haplotype specificity of the stigma. SLG is an abundant cell wall-associated glycoprotein similar in sequence to the extracellular domain of SRK.Among these pollen and stigma factors, SRK and SLG, the female factors, exhibited several features typical of SI factors. They are predominantly expressed in stigma papilla cells immediately prior to flower opening concomitant with the acquisition of SI in the stigma. Their sequence variations are correlated with the S-haplotypes. Following the accumulation of such circumstantial evidence, "gain-of-function" experiments employing transgenics established that SRK alone determines the S-haplotype specificity of the stigma, whereas SLG facilitates the recognition process (7). In contrast to these female factors, the identification of the male S determinant remained elusive. Two approaches were used for its eventual identification: one approach concerned the genome analysis of the Slocus region to identify genes specifically expressed in anthers (8), whereas the other employed a fluorescent differential display methodology to identify anther-expressed genes that were specific for the S-haplotype (9). These in...

High-resolution seismic reflection profiles delineated the distribution of moundshaped reflections, which were interpreted as reefs, beneath the insular shelf western off Irabu Island, Ryukyus, southwestern Japan. A sediment core through one of the mounded structures was recovered from the sea floor at a depth of −118.2 m by offshore drilling and was dated by radiometric methods. The lithology and coral fauna of the core indicate that the mounded structure was composed of coral-algal boundstone suggesting a small-scaled coral reef. High-precision α-spectrometric 230 Th/ 234 U dating coupled with calibrated accelerator mass spectrometric 14 C ages of corals obtained reliable ages of this reef ranging from 22.18 ± 0.63 to 30.47 ± 0.98 ka. This proves that such a submerged reef was formed during the lowstand stage of marine oxygen isotope stages 3-2. The existence of low-Mg calcite in the aragonitic coral skeleton of 22.18 ± 0.63 ka provides evidence that the reef had once been exposed by lowering of the relative sealevel to at least −126 m during the last glacial maximum in the study area. There is no room for doubt that a coral reef grew during the last glacial period on the shelf off Irabu Island of Ryukyus in the subtropical region of western Pacific.

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