An mRNA encoding a response regulator protein from Brassica napus is up-regulated during pod development

chemical changes take place, thus preparing both seeds and pod for the event. Shatter eventually occurs as a A novel cDNA (SAC29) was isolated by differential result of a combination of factors including: the creation display from pod dehiscence zone tissue during a of tensions within the pod between the lignified valve study directed at identifying genes expressed during edge cells of the endocarp and the unlignified dehiscence pod development in oilseed rape (Brassica napus L.). zone (DZ ) cells, weakening of the DZ cell walls by SAC29 encodes a 136 amino acid putative peptide, hydrolytic enzyme activity and, ultimately, due to physical which shows homology to various prokaryotic and forces such as strong winds or harvesting machinery. eukaryotic response regulator proteins. The homolog- Pod development in B. napus can be segmented into ous regions are centred about the four highly three stages. In the first stage, which occurs 0‐20 DAA, conserved amino acid residues of bacterial receivers the newly formed siliques, consisting of two seedincluding the aspartic acid motif required for phos- containing carpels separated by a false septum and a phorylation and subsequent transduction of the initial replar region, grow to their full length of around 10 cm. signal. Northern blot analysis of SAC29 showed hybrid- The seeds begin to grow when the pods are virtually full ization to a 0.6 kb transcript which was most abundant size (Hocking and Mason, 1993). Between 10 and 20 in RNA extracted from the dehiscence zone of pods at DAA the cells in the replar region begin to diVerentiate 40 d after anthesis. The role of SAC29 as a component into replar cells, large valve edge cells and form a distinct in a signalling cascade regulating dehiscence of the region, 1‐3 cells wide, comprising the DZ (Meakin and pod is discussed. Roberts, 1990a). The second stage occurs between 20 and 50 DAA.