SummarySGT1 (Suppressor of G2 allele of SKP1) is required to maintain plant disease Resistance (R) proteins with Nucleotide-Binding (NB) and Leucine-Rich Repeat (LRR) domains in an inactive but signaling-competent state. SGT1 is an integral component of a multi-protein network that includes RACK1, Rac1, RAR1, Rboh, HSP90 and HSP70, and in rice the Mitogen-Activated Protein Kinase (MAPK), OsMAPK6. Tobacco (Nicotiana tabacum) N protein, which belongs to the Toll-Interleukin Receptor (TIR)-NB-LRR class of R proteins, confers resistance to Tobacco Mosaic Virus (TMV).Following transient expression in planta, we analyzed the functional relationship between SGT1, SIPK -a tobacco MAPK6 ortholog -and N, using mass spectrometry, confocal microscopy and pathogen assays.Here, we show that tobacco SGT1 undergoes specific phosphorylation in a canonical MAPK target-motif by SIPK. Mutation of this motif to mimic SIPK phosphorylation leads to an increased proportion of cells displaying SGT1 nuclear accumulation and impairs N-mediated resistance to TMV, as does phospho-null substitution at the same residue. Forced nuclear localization of SGT1 causes N to be confined to nuclei.Our data suggest that one mode of regulating nucleocytoplasmic partitioning of R proteins is by maintaining appropriate levels of SGT1 phosphorylation catalyzed by plant MAPK.
To gain knowledge of root resistance mechanisms in sugar beet, Beta vulgaris L., our laboratory has been studying the interaction of sugar beet with its most devastating insect pest, the sugar beet root maggot (SBRM; Tetanops myopaeformis Roder). Damage from SBRM infestations is a serious problem and current control measures rely on environmentally damaging insecticides. We recently reported root-specific gene expression incited by SBRM feeding in a moderately resistant F1016 and a susceptible parental F1010 line. A cDNA expressed sequence tag (EST) coding for a serine (trypsin-type) protease inhibitor (BvSTI) was identified and investigated further here. BvSTI shares sequence similarity with a root-specific tomato gene whose expression is induced by insect feeding. Since serine proteases comprise the major digestive enzymes in root maggot midguts, we hypothesize BvSTI may be involved in resistance. To elucidate the functional role of BvSTI, its coding region was fused to the CaMV 35S promoter and constitutively expressed in sugar beet hairy roots and N. benthamiana plants. In BvSTItransformed F1010 hairy roots, trypsin inhibitory activity increased 2 to 4-fold. Using a polyacrylamide gel assay, new trypsin-like PI activity was detected in BvSTI-N. benthamiana plants. Since SBRM cannot be reared in vitro, two other insects that utilize serine digestive proteases, fall armyworm (Spodoptera frugiperda) and tobacco hornworm (Manduca sexta), were screened for resistance. To date, we demonstrated that 1) fall armyworm will feed on sugar beet hairy roots and 2) tobacco hornworm fed BvSTI-N. benthamiana leaves had reduced weights and pupal sizes. These results suggest that BvSTI may contribute to the moderate resistance of F1016 roots to SBRM. Functional analysis of additional ESTs will further support efforts to characterize the components of sugar beet root resistance mechanisms.
, "RNA polymerase II gene (RPB2) encoding the second largest protein subunit in Phaeosphaeria nodorum and P. avenaria" (2006 Size differences were found in the full length RPB2 gene of cereal Phaeosphaeria species, mainly due to differences in intron size. No nucleotide substitutions were found in homothallic P. avenaria f.sp. triticea (Pat1) and barley biotype P. nodorum (PN-b) isolates used in this study. The nucleotide and deduced amino acid sequences of the RPB2 gene in Pat1 were closely related to that in PN-w.
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