The identification of effectors from pathogenic microbes is one of the most important subjects for elucidating infection mechanisms. Wheat blue dwarf (WBD) phytoplasma causes dwarfism, witches' broom, and yellow leaf tips in wheat plants, resulting in severe yield loss in northwestern China. In this study, 37 candidate effector proteins were transiently expressed in Nicotiana benthamiana. Plants expressing the SAP11-like protein SWP1 exhibited typical witches' broom. Interestingly, another protein, SWP11, induced both cell death and defence responses, including H 2 O 2 accumulation and callose deposition. Analysis by qRT-PCR was used to show that a marker gene of the hypersensitive response, HIN1, and three pathogenesis-related genes, PR1, PR2 and PR3, were significantly up-regulated in leaves of N. benthamiana expressing SWP11. In addition, SWP12 and SWP21 (TENGU-like) were shown to suppress SWP11-, BAX-, and/or INF1-induced cell death. These results indicated that SWP21 has a distinct role in virulence compared with TENGU and that WBD phytoplasma possesses effectors that target plant proliferation and defence responses. The ability of these effectors to trigger or suppress plant immunity provides new insights into the phytoplasma-plant interaction.

Early leaf senescence in wheat (Triticum aestivum L.) is one of the limiting factors for developing high yield potential. In this study, a stably inherited, early leaf-senescence mutant LF2099 was initially identified in an M2 population of the common wheat accession H261 after ethyl methanesulfonate (EMS) mutagenesis. Early leaf senescence was observed in the LF2099 mutant during the three-leaf-stage, and then the etiolated area of the wheat leaf increased gradually from the bottom to the top throughout development. Compared with H261, the chlorophyll (Chl a, Chl b) and carotenoid contents and photosynthetic capacity of the mutant were significantly decreased. All of its yield-related traits except for spike length were also significantly reduced. Dissolved cytoplasm, abnormal chloroplast structure, dissolved chloroplast membrane, abnormal thylakoid development, and more plastoglobules were observed in the senescent leaf region of the mutant by transmission electronic microscope. Genetic analysis indicated that the early leaf-senescence phenotype is controlled by an incomplete-dominance nuclear gene, here designated Els2. Using single nucleotide polymorphisms and bulked segregant analysis, the els2 gene was anchored in a region on chromosome 2BL between simple sequence repeat (SSR) markers gpw4043 and wmc149. Six new polymorphic SSR markers were developed from the Chinese Spring 2BL shotgun survey sequence contigs. By means of comparative genomics analyses, the collinearity genomic regions of the els2 locus on wheat 2BL were identified in Brachypodium distachyon chromosome 5, rice (Oryza sativa) chromosome 4 and sorghum (Sorghum bicolor) chromosome 6. Five intron polymorphism (IP) markers were further developed from this collinearity genomic region. Ultimately, Els2 was mapped in a genetic interval of 0.95 cM flanked by IP markers 2BIP09 and 2BIP14. The co-segregating IP markers 2BIP12 and 2BIP17 provide a starting point for the fine mapping and map-based cloning of Els2.

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The yellow–green leaf mutant can be exploited in photosynthesis and plant development research. A Triticum aestivum mutant with the chlorina phenotype, here called B23, was produced by treatment with the chemical mutagen sodium azide. This B23 mutant showed significantly lower chlorophyll content than wild-type Saannong33, and its chloroplast structure was abnormal. All its yield-related traits, except for the number of spikes per plant, were also significantly decreased. Genetic analysis confirmed that the mutant phenotype was controlled by a recessive gene, here designated cn-A1. Using bulked segregant analysis and the wheat 660K single nucleotide polymorphism array, the cn-A1 gene was mapped to chromosome 7AL, and 11 polymorphic markers were developed. Further analysis showed that cn-A1 was located in a 1.1-cM genetic region flanked by Kompetitive allele specific PCR (KASP) markers 660K-7A12 and 660K-7A20, which corresponded to a physical interval of 3.48 Mb in T. aestivum cv. Chinese Spring chromosome 7AL containing 47 predicted genes with high confidence. These results are expected to accelerate the process of cloning the cn-A1 gene and facilitate understanding of the mechanisms underlying chlorophyll metabolism and chloroplast development in wheat.

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Eight cultivars of dry-land wheat (Triticum aestivum L.) historically planted in Shaanxi Province, China, were grown in plots with irrigation and drought treatments during the growing seasons of 2011-2014, so as to characterize the differences in the rate and duration of the grain-filling stage among cultivars. The experimental results showed no obvious change among cultivars with respect to the duration of the grain-filling stage and no significant correlation between duration and grain weight. The filling rates of all three phases (lag, linear, and mature periods) showed significant differences among cultivars and had a greater effect on the grain weight than the duration of the filling stage, even though drought decreased the filling rate in the linear and mature periods. A lower filling rate led to a lighter grain weight in inferior grains than in superior grains. For the superior and inferior grains in the central spikelets, modern cultivars possess faster filling rates, especially in the lag and linear periods, whereas for the whole spike, no significant trend with cultivar replacement was observed. Faster filling rates with stable filling durations will be beneficial in obtaining additional yield increases.Abbreviations: FRa, filling rate, average; FD, filling duration; FR1, filling rate in 1st period (lag period); FD1, filling duration in 1st period (lag period); FR2, filling rate in 2nd period (linger period); FD2, filling duration in 2nd period (linear period); FR3, filling rate in 3rd period (mature period); FD3, filling duration in 3rd period (mature period).