The Pseudomonas syringae hrp and hrmA genes controlling pathogenicity and elicitation of the hypersensitive response and the avr genes controlling host range have been shown previously to be regulated by carbon, nitrogen, pH, osmolarity, and hypothetical plant factors. In P. syringae pv. syringae Pss6l, inactivation of hrp complementation groups II and XIII reduced expression of a plasmid-borne hrmA'-lacZ fusion. The hrp regions II and XIII were cloned on separate plasmids and shown to enhance the activity of the hrmA promoter in Escherichia coli MC4100 transformants at least 100-fold. The nucleotide sequence of region XIII revealed two open reading frames (hrpR and hrpS) whose deduced products share homology with P. syringae pv. phaseolicola NPS3121 HrpS and are both related to the NtrC family of two-component signal transduction systems. HrpR and HrpS differ from most members of the protein family by lacking an amino-terminal domain which modulates the regulatory activity. A single open reading frame, hrpL, whose product shares homology with AlgU, a putative alternate sigma factor of P. aeruginosa, as well as with the related alternate sigma factors was identified. within region II. Key domains are partially conserved. Inactivation of hrpS in Pss6l repressed expression of a plasmid-borne hrpL'-lacZ fusion carried by pYXPLlR, and transformation of MC4100(pYXPL1R) with a plasmid carrying hrpRS increased hrpL promoter activity at least 200-fold. Neither hrpS nor hrpR, when cloned on separate plasmids, activated the hrpL promoter activity individually. The expression of hrpL when directed by a lac promoter was sufficient to express a set of plasmid-borne hrmA'-, hrpJ'-, and hrpZ'-lacZ fusions independently of other hrp genes. The results indicate that hrpRS and hrpL are part of a regulatory cascade in which HrpR and HrpS activate expression of hrpL and HrpL, a putative sigma factor, induces expression of HrpL-responsive genes.

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The ability of Pseudomonas syringae pv. syringae 61 to elicit the hypersensitive response in nonhost plant species has been linked to a cluster ofhrplhrm genes whose expression appears to be environmentally regulated.To understand the genetic organization of this hrplhrrn gene cluster and its expression during the interaction with nonhost plant species better, we constructed a set of chromosomal hrp-uidA fusions in P. syringae pv.syringae 61 by Tn5-gusAl mutagenesis of the cloned hrp/hrm gene cluster and transferred them into the genome by marker exchange mutagenesis. Complementation analysis employing plasmid-borne Tn5-gusA4 insertions and previously characterized chromosomal TnphoA mutations defined at least eight apparent transcriptional units within the hrplhrm cluster, several of which were multicistronic. The expression of hrp-uid4 fusions in seven of these apparent hrp transcriptional units increased following inoculation into tobacco leaves. Enhanced expression from a representative fusion was detected 1 h after inoculation of tobacco leaves. The induction observed in planta was similar to the levels detected following culture of the bacteria in minimal-salts medium: irrespective of the carbon source. Complex amino acid sources, such as peptone, repressed the expression of P. syringae pv. syringae 61 hrp genes at levels exceeding 0.028%. The results indicate that enhanced expression of hrp genes occurs early in the interaction with nonhost plant species in an apparent response to altered nutritional conditions. The hypersensitive response (HR) is a rapid, localized necrosis of plant tissue that is observed when strains of Pseudomonas syringae are inoculated into nonhost plant species or resistant varieties of susceptible plant species (24). The HR appears to be a manifestation of localized plant defense mechanisms initiated by a postulated recognition event between P. syringae and a resistant host plant (7,(20)(21)(22). The recognition process requires a 2-to 4-h induction stage during which the plant response is sensitive to inhibitors of bacterial transcription and translation (24,41). This suggests that bacterial gene expression induced in response to an undefined environmental signal during the initial 2 to 4 h of the interaction may be necessary to elicit the HR (17,22,41

Available online A B S T R A C TWhole wheat provides a rich source of bioactive phytochemicals namely, phenolic acids, carotenoids, tocopherols, alkylresorcinols, benzoxazinoids, phytosterols, and lignans. This review provides information on the distribution, extractability, analysis, and functional properties of bioactive phytochemicals present in wheat. Understanding the impact of processing on wheat phytochemicals allows us to develop improved processes with higher retention of bioactive compounds in processed wheat foods. Details of extraction, analytical methodologies and processing effects on bioactive phytochemicals in wheat are presented in tabulated form.Published by Elsevier Ltd.