Accelerated molecular breeding of a novel P/TGMS line with broad-spectrum resistance to rice blast and bacterial blight in two-line hybrid rice.

BACKGROUND: Breeding two-line hybrid rice with disease resistance is an effective approach to stabilize rice yield in commercial rice production of China. RESULTS: We improved the blast and bacterial blight resistance of Guangzhan63-4S, an elite photoperiod- and thermo-sensitive male sterile (P/TGMS) line widely used in two-line hybrid rice, by introducing the R genes Pi2 and Xa7 conferring resistance to rice blast and bacterial blight, respectively. Through the backcrossing and gene pyramiding breeding coupled with molecular marker-assisted selection, a new P/TGMS line Hua1228S carrying Pi2, Xa7, and tms5 was developed. Based on 200,000 SNP markers by next-generation sequencing, Hua1228S covered 87.6% of the recurrent genome, as well as 4.5% of the donor genome from VE6219 and 7.9% from YR7029-39. When infected with seven tested Xanthomonas oryzae pv. oryzae strains, Hua1228S conferred high resistance (0 level) to six bacterial blight strains. Moreover, Hua1228S showed broad-spectrum resistance to rice blast isolates with a high resistance frequency of 90.91%. High levels of resistance to leaf blast and neck blast were observed under heavy disease pressure in natural field. Importantly, Hua1228S showed identical fertility-sterility alteration pattern to Guangzhan63-4S. Thus, two hybrid combinations Hua Liangyou 2821 and Hua Liangyou 284 derived from Hua1228S exhibited enhanced resistance and higher yield compared with the control variety Feng Liangyou 4. CONCLUSIONS: These results indicate that Hua1228S has tremendous potentiality to increase and stabilize the rice yield, through the introgression of two R genes by marker-assisted selection strategy.

A re-sequencing-based ultra-dense genetic map reveals a gummy stem blight resistance-associated gene in Cucumis melo.

The melon (Cucumis melo) genome and genetic maps with hundreds to thousands of single nucleotide polymorphism markers were recently released. However, a high-resolution genetic map was lacking. Gummy stem blight (Gsb) is a destructive disease responsible for considerable economic losses during melon production. We herein describe the development of an ultra-dense genetic map consisting of 12,932 recombination bin markers covering 1,818 cM, with an average distance of 0.17 cM between adjacent tags. A comparison of the genetic maps for melon, watermelon, and cucumber revealed chromosome-level syntenic relationships and recombination events among the three Cucurbitaceae species. Our genetic map was useful for re-anchoring the genome scaffolds of melon. More than 92% assembly was anchored to 12 pseudo-chromosomes and 90% of them were oriented. Furthermore, 1,135 recombination hotspots revealed an unbalanced recombination rate across the melon genome. Genetic analyses of the Gsb-resistant and -susceptible lines indicated the resistance phenotype is mediated by a single dominant gene. We identified Gsb-resistance gene candidates in a 108-kb region on pseudo-chromosome 4. Our findings verify the utility of an ultra-dense genetic map for mapping a gene of interest, and for identifying new disease resistant genes.

Eukaryotic translation initiation factor 2B-beta (eIF2Bß), a new class of plant virus resistance gene.

Recessive resistances to plant viruses in the Potyvirus genus have been found to be based on mutations in the plant eukaryotic translation initiation factors, eIF4E and eIF4G or their isoforms. Here we report that natural, monogenic recessive resistance to the Potyvirus Turnip mosaic virus (TuMV) has been found in a number of mustard (Brassica juncea) accessions. Bulked segregant analysis and sequencing of resistant and susceptible plant lines indicated the resistance is controlled by a single recessive gene, recessive TuMV resistance 03 (retr03), an allele of the eukaryotic translation initiation factor 2B-beta (eIF2Bß). Silencing of eIF2Bß in a TuMV-susceptible mustard plant line and expression of eIF2Bß from a TuMV-susceptible line in a TuMV-resistant mustard plant line confirmed the new resistance mechanism. A functional copy of a specific allele of eIF2Bß is required for efficient TuMV infection. eIF2Bß represents a new class of virus resistance gene conferring resistance to any pathogen. eIF2B acts as a guanine nucleotide exchange factor (GEF) for its GTP-binding protein partner eIF2 via interaction with eIF2·GTP at an early step in translation initiation. Further genotyping indicated that a single non-synonymous substitution (A120G) in the N-terminal region of eIF2Bß was responsible for the TuMV resistance. A reproducible marker has been developed, facilitating marker-assisted selection for TuMV resistance in B. juncea. Our findings provide a new target for seeking natural resistance to potyviruses and new opportunities for the control of potyviruses using genome editing techniques targeted on eIF2Bß.