A NAC Transcription Factor TuNAC69 Contributes to ANK-NLR-WRKY NLR-Mediated Stripe Rust Resistance in the Diploid Wheat Triticum urartu

Stripe rust is one of the most devastating diseases in wheat. Nucleotide-binding site (NBS) and leucine-rich repeat (LRR) domain receptors (NLRs) recognize pathogenic effectors and trigger plant immunity. We previously identified a unique NLR protein YrU1 in the diploid wheat Triticum urartu, which contains an N-terminal ANK domain and a C-terminal WRKY domain and confers disease resistance to stripe rust fungus Puccinia striiformis f. sp. Tritici (Pst). However, how YrU1 functions in disease resistance is not clear. In this study, through the RNA-seq analysis, we found that the expression of a NAC member TuNAC69 was significantly up-regulated after inoculation with Pst in the presence of YrU1. TuNAC69 was mainly localized in the nucleus and showed transcriptional activation in yeast. Knockdown TuNAC69 in diploid wheat Triticum urartu PI428309 that contains YrU1 by virus-induced gene silencing reduced the resistance to stripe rust. In addition, overexpression of TuNAC69 in Arabidopsis enhanced the resistance to powdery mildew Golovinomyces cichoracearum. In summary, our study indicates that TuNAC69 participates in the immune response mediated by NLR protein YrU1, and likely plays an important role in disease resistance to other pathogens.

Introgression of the Powdery Mildew Resistance Genes Pm60 and Pm60b from Triticum urartu to Common Wheat Using Durum as a ‘Bridge’

Powdery mildew, caused by the fungus Blumeria graminis f. sp. tritici (Bgt), has limited wheat yields in many major wheat-production areas across the world. Introducing resistance genes from wild relatives into cultivated wheat can enrich the genetic resources for disease resistance breeding. The powdery mildew resistance gene Pm60 was first identified in diploid wild wheat Triticum urartu (T. urartu). In this study, we used durum as a ‘bridge’ approach to transfer Pm60 and Pm60b into hexaploid common wheat. Synthetic hexaploid wheat (SHW, AABBAuAu), developed by crossing T. urartu (AuAu) with durum (AABB), was used for crossing and backcrossing with common wheat. The Pm60 alleles were tracked by molecular markers and the resistance to powdery mildew. From BC1F1 backcross populations, eight recombinant types were identified based on five Pm60-flanking markers, which indicated different sizes of the introgressed chromosome segments from T. urartu. Moreover, we have selected two resistance-harboring introgression lines with high self-fertility, which could be easily used in wheat breeding system. Our results showed that the durum was an excellent ‘bridge’ for introducing the target gene from diploid T. urartu into the hexaploid cultivated wheat. Moreover, these introgression lines could be deployed in wheat resistance breeding programs, together with the assistance of the molecular markers for Pm60 alleles.

The Wild Emmer Wheat Gene PmG16, Conferring Resistance to Powdery Mildew, is an Orthologue of Pm60 from Triticum Urartu

Wild emmer wheat (WEW), the tetraploid progenitor of durum and bread wheat, is a valuable genetic resource for resistance to powdery mildew fungal disease caused by Blumeria graminis f. sp. tritici (Bgt). PmG16 gene, derived from WEW, confers high resistance to most tested Bgt isolates. We mapped PmG16 to a 1.4 cM interval between the flanking markers uhw386 and uhw390 on Chromosome 7AL. Based on gene annotation of WEW reference genome Zavitan_V1, 34 predicted genes were identified within the ~3.48 Mb target region. Six genes were annotated as associated with disease resistance, of which TRIDC7AG077150.1 was found to be highly similar to Pm60, previously cloned from Triticum urartu and residing in the same syntenic region. A functional molecular marker (FMM) for Pm60 (M-Pm60-S1) co-segregated with PmG16, suggesting that WEW PmG16 is probably an orthologue of Pm60 from Triticum urartu (designated here as TdPm60). Sequence alignment identified only eight SNPs that differentiate between TdPm60 and TuPm60. Furthermore, our results suggest that other WEW powdery mildew resistance genes MlIW172 and MlIW72, that also mapped to the same region of Chromosome 7AL, might be identical or allelic to TdPm60. Screening of 230 WEW accessions with Pm60 specific markers, 58 resistant accessions were identified from Southern Levant harboring the TdPm60 allele, while all the susceptible accessions showed no PCR amplifications. Deployment of TdPm60 is clearly more advantageous over TuPm60 since it can be rapidly introgressed by classical breeding approaches into bread wheat genetic background.

Ecological assembly processes of the bacterial and fungal microbiota of wild and domesticated wheat species

Plant domestication has led to substantial changes in the host physiology. How this anthropogenic intervention has contributed in altering the wheat microbiota is not well understood. Here, we investigated the role of ecological selection, drift and dispersal in shaping the bacterial and fungal communities associated with domesticated wheat Triticum aestivum and two wild relatives, Triticum boeoticum and Triticum urartu. Our study shows that the bacterial and fungal microbiota of wild and domesticated wheat species follow distinct community assembly patterns. Further, we revealed a more prominent role of neutral processes in the assembly of the microbiota of domesticated wheat and propose that domestication has relaxed selective processes in the assembly of the wheat microbiota.