Genetic diversity of Ustilago hordei in Tibetan areas as revealed by RAPD and SSR

Covered smut, which is caused by Ustilago hordei（Pers.） Lagerh., is one of the most damaging diseases of highland barley（Hordeum vulgare Linn. var. nudum Hook. f） in Tibetan areas of China. To understand the molecular diversity of U. hordei, a total of 27 isolates, which were collected from highland barley plants from Tibet, Sichuan, Qinghai, and Gansu provinces/autonomous region, were analyzed using random amplified polymorphic DNA（RAPD） and simple sequence repeat（SSR） markers. Among the 100 RAPD primers used, 24 primers exhibited polymorphism. A total of 111 fragments were amplified, of which 103 were polymorphic with a polymorphic rate of 92.79%. The average observed number of alleles（Na）, effective number of alleles（Ne）, Nei＇s genetic diversity（H）, Shannon＇s information index（I） and polymorphism information content（PIC） value in the RAPD markers were 1.9279, 1.5016, 0.2974, 0.4503 and 0.6428, respectively. For the SSR markers, 40 of the 111 primer pairs exhibited polymorphism and provided a total of 119 bands, of which 109 were polymorphic and accounted for 91.60% of the total bands. The Na, Ne, H, I and PIC values of the SSR markers were 1.9160, 1.4639, 0.2757, 0.4211 and 0.4340, respectively. The similarity coefficients ranged from 0.4957 to 0.9261 with an average of 0.7028 among all the 27 isolates used. The dendrogram, which was developed based on the RAPD and SSR combined marker dataset showed that the 27 U. hordei isolates were divided into 3 clusters at similarity coefficient of 0.7314. We determined that RAPD and SSR markers can be successfully used to assess the genetic variation among U. hordei isolates. The RAPD markers revealed higher levels of genetic polymorphism than did the SSR markers in this study. There existed a moderate genetic difference among isolates. The molecular variation and differentiation was somewhat associated with geographical origin but not for all of the isolates.

Vacuolar processing enzyme positively modulates plant resistance and cell death in response to Phytophthora parasitica infection

Oomycete, particularly Phytophthora species, causes the most devastating crop diseases, such as potato late blight,and threatens the sustainable crop production worldwide. Our previous studies identified Resistance to Phytophthora parasitica 1(RTP1) as a negative regulator of Arabidopsis resistance to multiple biotrophic pathogens and RTP1 lossof-function plants displayed rapid cell death and reactive oxygen species(ROS) production during early colonization of P. parasitica. In this study, we aim to decipher the mechanism of RTP1-mediated cell death, and identify a member of vaculoar processing enzymes(VPEs), γVPE, playing a role in rtp1-mediated resistance to P. parasitica and cell death occurrence. Our results showed up-regulation of the expression of γVPE as well as increased VPE/caspase 1-like protease activity in P. parasitica-infected rtp1 mutant plants. Besides, we found that the VPE/caspase 1-like protease activity was required for the cell death occurrence in Arabidopsis plants during the infection of P. parasitica as well as rtp1-mediated resistance to P. parasitica. Further pathogenicity assays on either Arabidopsis γvpe mutant plants or leaves of Nicotiana benthamiana with transient overexpression of γVPE demonstrated γVPE could positively affect plant resistance to P. parasitica. Together, our studies suggest that γVPE might function as an important regulator of plant defense and cell death occurrence in response to P. parasitica infection, and VPE/caspase 1-like protease activity is required for rtp1-mediated resistance to P. parasitica.

Identification of genetic locus with resistance to take-all in the wheat-Psathyrostachys huashanica Keng introgression line H148

Take-all is a devastating soil-borne disease of wheat(Triticum aestivum L.).Cultivating resistant line is an important measure to control this disease.Psathyrostachys huashanica Keng is a valuable germplasm resource with high resistance to take-all.This study reported on a wheat-/R huashanica introgression line H148 with improved take-all resistance compared with its susceptible parent 7182.To elucidate the genetic mechanism of resistance in H148,the F_(2)genetic segregating population of H148×XN585 was constructed.The mixed genetic model analysis showed that the take-all resistance was controlled by two major genes with additive,dominant and epistasis effects.Bulked segregant analysis combined with wheat axiom 660K genotyping array analysis showed the polymorphic SNPs with take-all resistance from P.huashanica alien introgression were mainly distributed on the chromosome 2A.Genotyping of the F_(2)population using the KASP marker mapped a major QTL in an interval of 68.8-70.1 Mb on 2AS.Sixty-two genes were found in the target interval of the Chinese Spring reference genome sequence.According to the functional annotation of genes,two protein genes that can improve the systematic resistance of plant roots were predicted as candidate genes.The development of wheat-P.huashanica introgression line H148 and the resistant QTL mapping information are expected to provide some valuable references for the fine mapping of disease-resistance gene and development of take-all resistant varieties through molecular marker-assisted selection.