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The tropical staple cassava is subject to several major diseases, such as cassava bacterial blight, caused byXanthomonas axonopodispv.manihotis. Disease-resistant genotypes afford the only practical solution, yet despite the global importance of this crop, little is known about its defence mechanisms. cDNA-AFLP was used to isolate cassava genes differentially expressed during the hypersensitive reaction (HR) of leaves in response to an incompatiblePseudomonas syringaepathovar. Seventy-eight transcript-derived fragments (TDFs) showing differential expression (c. 75% up-regulated, 25% down-regulated) were identified. Many encoded putative homologues of known defence-related genes involved in signalling (e.g. calcium transport and binding, ACC oxidases and a WRKY transcription factor), cell wall strengthening (e.g. cinnamoyl coenzyme A reductase and peroxidase), programmed cell death (e.g. proteases, 26S proteosome), antimicrobial activity (e.g. proteases andβ-1,3-glucanases) and the production of antimicrobial compounds (e.g. DAHP synthase and cytochrome P450s). Full-length cDNAs including a probable matrix metalloprotease and a WRKY transcription factor were isolated from six TDFs. RT-PCR or Northern blot analysis showed HR-induced TDFs were maximally expressed at 24 h, although some were produced by 6 h; some were induced, albeit more slowly, in response to wounding. This work begins to reveal potential defence-related genes of this understudied, major crop. [ABSTRACT FROM AUTHOR]

The article shows that the genes yjbE, yjbF, yjbG and yjbH are transcribed as a single operon and it is confirmed that the expression of this operon is controlled by the Rcs phosphorelay. The RcsCDB phosphorelay was originally identified as the main regulator of colanic acid biosynthesis in Escherichia coli K-12. The article provides evidence that the overexpression of yjbEFGH affects colony morphology.