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The stay-green mutant of Arabidopsis thaliana, ore10 forms stable light-harvesting complex II (LHCII) aggregates during dark-induced senescence, which showed a single base deletion (G1351) in the coding region of the pheophytinase (PPH) gene. PPH specifically dephytylates the Mg-free chlorophyll (Chl) pigment pheophytin, yielding pheophorbide. In both ore10 and pph-1 mutants, pheophytin a accumulated due to the deficiency of PPH gene, but the amount was relatively smaller than that of degraded Chl, and most of the pheophytin a was bound to the stable LHCII forming aggregates with some other Chl-protein (CP) complexes. Comparison of Chl a/b ratios in thylakoids, aggregates, and LHCII indicated that the suppression of Chl b to Chl a conversion was stronger when Chl b reductase was missing and weak when PPH is missing in the large Chl catabolic complex, which allowed the partial degradation of Chl b. These results suggest that the PPH-dependent pathway is not specific for LHCII, but common for all CP complexes, including LHCII. In PPH-deficient mutants, the degradation of LHCII was suppressed by the formation of aggregates, and some of the remaining CP complexes and pheophytin a were included in the aggregates. Non-included CP complexes were degraded via an unknown mechanism.

Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most serious diseases in wheat (Triticum aestivum) and barley (Hordeum vulgare). Dahongmil is an elite Korean wheat cultivar with relatively high resistance to FHB. To identify differentially expressed genes in the resistant cultivar Dahongmil and the susceptible cultivar Urimil after inoculation of F. graminearum, we used the Affymetrix GeneChip® Wheat Genome Array to identify 328 ESTs that were differentially expressed in inoculated seedling tissues of the two cultivars. From these, we selected 16 induced genes and found that they have defense functions, such as genes encoding pathogen resistance proteins, oxidative stress-related proteins, metabolism, and proteins involved in defense mechanisms. To verify the DNA microarray results, we tested seven of these genes by semiquantitative RT-PCR and confirmed that these defense- and stress-related genes were expressed at much higher levels in the resistant Dahongmil cultivar. We next developed a hypothetical functional gene network and identified 89 interaction pairs mediated by four of the differentially expressed genes in the hypothetical network. We further refined the network by identifying nine genes showing significant up- or down-regulation after FHB challenge in the resistant cultivar and two genes having multiple interactions with queried proteins. We hope that the set of induced genes identified in this study can be used for development of new wheat and barley cultivars with improved resistance to FHB.

Tillering in rice (Oryza sativa L.) is an important agronomic trait that enhances grain production. A tiller is a specialized grain-bearing branch that is formed on a non-elongated basal internode that grows independently of the mother stem. Transgenic rice over-expressing the transcription factorOsTB1, a homologue of maizeTB1 (Teosinte Branched 1), exhibits markedly reduced lateral branching without the propagation of axillary buds being affected. However, the tillering mechanism remains unknown. Therefore, to further understand that mechanism, we applied proteomics methodology to isolate the proteins involved. Using two-dimensional gel electrophoresis and mass spectrometry, our analysis of the basal nodes from two rice cultivars that differ in their numbers of tillers showed that a rice serine proteinase inhibitor, OsSerpin, accumulates in great amounts in high-tillering ‘Hwachung’ rice. Northern blot analysis revealed that much moreOsSerpin transcript is found in ‘Hwachung’ than in relatively low-tillering ‘Hanmaeum’, likely because of high levels of transcription. Therefore, our data suggest that OsSerpin content determines the extent of lateral branching.

The identification of molecular markers and marker-aided selection are essential to the efficient breeding of drought-tolerant plants. However, because that characteristic is controlled by many quantitative trait loci, such markers that can screen and trace desirable barley genotypes in a segregating population or germplasm have not yet been determined. Relative water content has been used to estimate drought tolerance in plants because it is highly correlated with the drought index of yield. To develop reliable gene-specific markers for identifying tolerant versus susceptible genotypes, we performed suppression subtractive hybridization to identify candidate genes. We used two domestic barley cultivars, one having the highest RWC (drought-tolerant ‘Chalbori’) and the other having the lowest (drought-susceptible ‘Daebaekbori’). In response to dehydration at the early seedling stage, rapid upregulation ofDehydrin3 (Dhn3) andDhn4 occurred in the drought-tolerant genotypes, but not in the susceptible ones. Similar results were obtained with mature plants growing under frequent drought stress in the greenhouse. In addition,Dhn3 andDhn4 conferred higher drought tolerance when they were over-expressed in transgenicArabidopsis. Thus, in addition to using assessments of RWC, we propose thatDhn3 andDhn4 expressions can serve as drought-induced gene-specific markers to determine drought-tolerant barley genotypes at the seedling stage.