We have identified a recurrent de novo pericentromeric deletion in 16p11.2-p12.2 in four individuals with developmental disabilities by microarray-based comparative genomic hybridization analysis. The identification of common clinical features in these four individuals along with the characterization of complex segmental duplications flanking the deletion regions suggests that nonallelic homologous recombination mediated these rearrangements and that deletions in 16p11.2-p12.2 constitute a previously undescribed syndrome.

Pod shatter in oilseed rape is associated with the degradation of the pectin-rich middle lamella at the site of dehiscence. It has been reported that, accompanying pod development, there is an increase in the activity of polygalacturonase (EC 3.2.1.15) and that this rise is restricted to the tissue undergoing cell separation. Using a PCR strategy a fragment of a polygalacturonase encoding an mRNA that is up-regulated specifically in the dehiscence zone tissue during pod development has been cloned. A full length clone (SAC66) complementary to this mRNA has been isolated from a dehiscence zone cDNA library and sequenced. The mRNA encoded by SAC66 shares significant amino acid homology with endopolygalacturonases from fruit of Actinidia deliciosa and Lycopersicon esculentum. The transcript size of the SAC66 mRNA is 1.7 kb. Northern analysis has revealed that expression of SAC66 mRNA increases at 30 d after anthesis (DAA), reaching a plateau at 45 DAA, and that the up-regulation is restricted to the site where dehiscence takes place.

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Pod dehiscence in Arabidopsis thaliana is accompanied by an increase in the expression of a polygalacturonase (PG).The gene encoding this mRNA has been characterized and shown to have extensive homology to a similar PG gene from Brassica napus. The A. thaliana PG promoter was fused to β-glucuronidase (GUS) and the expression of this reporter gene analysed in transgenic B. napus plants. The GUS activity was detected throughout the dehiscence zone of pods from 35 d after anthesis and expression was restricted to those cells that undergo cell separation. Expression was also detectable at the junction between the seed and the funicular tissue and in mature anthers of flowers. Transgenic plants containing the PG promoter fused to barnase were sterile as a consequence of the anthers failing to undergo dehiscence. Fertilization of PGbarnase plants resulted in the development of pods that exhibited a reduced capacity to shatter. The role of PG during cell separation processes in plants is discussed.Key-words: Arabidopsis thaliana; Brassica napus; oilseed rape; pod dehiscence; pod shatter; polygalacturonase. Genbank accession number AF037367 INTRODUCTIONPod dehiscence is the process that results in the premature shedding of seeds from siliques prior to and during harvest. The phenomenon of shatter, as it is more commonly termed, can cause major reductions in seed yield (MacLeod 1981) and has been identified as one of the major constraints limiting the further development of the oilseed crop world-wide.Pod shatter shares a number of features in common with the abscission process that leads to the shedding of leaves, flowers and fruits (Sexton & Roberts 1982; GonzalezCarranza, Loyoza-Gloria, & Roberts 1998). For instance, both dehiscence and abscission are the consequence of cell wall dissolution at a predetermined position (Sexton & Roberts 1982;Meakin & Roberts 1990a). Moreover, this event is the culmination of a highly co-ordinated series of cellular and molecular events that are restricted to the site where cell separation takes place (Coupe et al. , 1994Gonzalez-Carranza et al. 1998).There is a considerable body of evidence to support the hypothesis that both dehiscence and abscission are brought about by the action of cell wall hydrolases such as β-1,4 glucanase (EC 3·1.2·4) (Meakin & Roberts 1990b;Webb et al. 1993) and polygalacturonase (PG, EC 3·2.1·15) (Meakin & Roberts 1991;Taylor et al. 1993;Peterson et al. 1996). Recently the expression of a gene encoding an endo-PG (SAC66), which may be important for solubilizing pectin, has been shown by Northern analysis to increase in the region of B. napus pods where cell separation occurs at the time of shatter (Jenkins et al. 1996;Peterson et al. 1996). Southern analysis indicates that this gene is a member of a small gene family in B. napus (Jenkins et al. 1996) whilst in Arabidopsis thaliana it is represented by only a single gene (Jenkins 1997). In this paper we report the isolation of the homologous gene from A. thaliana and the characterization of its promo...