De novo Transcriptome Analysis in Leymus mollis to Unveil Genes Involved in Salt Stress Response

Leymus mollis,a wild relative of wheat,is very tolerant to salt stress,and has been considered as a valuable genetic resource for wheat breeding.However,the genetic basis for salt tolerance of this species is still largely unknown.In this study,de novo sequencing,assembly and analysis of L.mollis transcriptome in response to salt stress was performed.A total of 110,323 and 112,846 unigenes were generated for the NaCl-free(CK)and 180 mM NaCl-treated(CT)library,respectively.For the two libraries,73,414 unigenes were successfully annotated in five common protein databases,and 7521 differentially expressed genes(DEGs)between CK and CT libraries were identified.GO enrichment analysis of the DEGs showed that the significantly enriched GO terms were predominantly involved in environmental adaptation(including“response to abiotic stimulus”,“response to water deprivation”),regulation of signaling pathway(such as“regulation of abscisic acid mediated signaling pathway”,“regulation of cell communication”),and photosynthesis(including“response to light stimulus”,“photosynthesis,light harvesting”and“chlorophyll metabolic process”).KEGG pathway enrichment analysis showed that“mRNA surveillance pathway”,“RNA transport”and“plant hormone signal transduction”were predominantly enriched pathways,followed by several secondary metabolic pathways,photosynthesis,carbohydrate metabolism and lipid metabolism.In addition,DEGs related to osmotic stress,ion homeostasis and oxidative stress,including four dehydrins,five aquaporins,an LmNHX2 and several antioxidant enzymes or proteins genes,were found to be up-regulated in response to salt stress.These results will be helpful for further studies on the molecular mechanisms of salt responses in L.mollis.

Molecular Cytogenetic Characterization of a Wheat-Leymus mollis 3D(3Ns) Substitution Line with Resistance to Leaf Rust

Leymus mollis （Trin.） Pilger （NsNsXmXm, 2n = 28）, a wild relative of common wheat, possesses many potentially valuable traits that could be transferred to common wheat during breeding programs. In this study, the karyotypic constitution of a wheat - L. mollis 3D（3Ns#1） disomic substitution line isolated from the F5 progeny of octoploid Tritileymus M842-16 x Triticum durum cv. D4286, which was designated as 10DM57, was determined using genomic in situ hybridization （GISH）, fluorescent in situ hybridization （FISH）, SSR markers, and EST- STS markers. Screening of mitosis and meiosis showed that 10DM57 had a chromosome karyotype of 2n = 42 =21Ⅱ. GISH indicated that 10DM57 was a line with 40 chromosomes from wheat and two of the Ns chromosomes from L. mollis, which formed a ring bivalent in pollen mother cells at metaphase I. FISH analysis showed that the chromosome 3D may be replaced by 3Ns#1 in 10DM57. DNA markers, including SSR and EST-STS primers, showed that the pair of wheat chromosome 3D in 10DM57 was substituted by the pair of chromosome 3Ns#t from L. mollis. Evaluation of the agronomic traits showed that, compared with its common wheat relative 7182, 10DM57 was resistant to leaf rust while the spike length and number of spikes per plant were improved significantly, which correlated with a higher wheat yield. The new germplasm, 10DM57, could be exploited as an intermediate material in wheat genetic and breeding programs.

Development of Triticum aestivume——Leymus mollis Translocation Lines and Identification of Resistance to Stripe Rust

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most widely distributed and destructive fungal diseases worldwide. Since 1995, most Chinese wheat cultivars have lost their stripe rust resistance due to the subsequent emergence of the new races CYR30, CYR31, CYR32, and CYR33 （Han et al., 2010）. Therefore, it is necessary to seek effective resistance genes and develop new resistance germ- plasm for wheat resistance breeding.