The NLP toxin family in Phytophthora sojae includes rapidly evolving groups that lack necrosis-inducing activity.

Necrosis- and ethylene-inducing-like proteins (NLP) are widely distributed in eukaryotic and prokaryotic plant pathogens and are considered to be important virulence factors. We identified, in total, 70 potential Phytophthora sojae NLP genes but 37 were designated as pseudogenes. Sequence alignment of the remaining 33 NLP delineated six groups. Three of these groups include proteins with an intact heptapeptide (Gly-His-Arg-His-Asp-Trp-Glu) motif, which is important for necrosis-inducing activity, whereas the motif is not conserved in the other groups. In total, 19 representative NLP genes were assessed for necrosis-inducing activity by heterologous expression in Nicotiana benthamiana. Surprisingly, only eight genes triggered cell death. The expression of the NLP genes in P. sojae was examined, distinguishing 20 expressed and 13 nonexpressed NLP genes. Real-time reverse-transcriptase polymerase chain reaction results indicate that most NLP are highly expressed during cyst germination and infection stages. Amino acid substitution ratios (Ka/Ks) of 33 NLP sequences from four different P. sojae strains resulted in identification of positive selection sites in a distinct NLP group. Overall, our study indicates that expansion and pseudogenization of the P. sojae NLP family results from an ongoing birth-and-death process, and that varying patterns of expression, necrosis-inducing activity, and positive selection suggest that NLP have diversified in function.

A fast-neutron induced chromosome fragment deletion of 3BS in wheat landrace Wangshuibai increased its susceptibility to Fusarium head blight.

Fusarium head blight (FHB), also called wheat scab, is an important disease in warm and humid regions worldwide, which not only reduces crop yield and grain quality, but also is a major safety concern in food and feed production due to mycotoxin contamination. Growing wheat cultivars with FHB resistance is one of the most economical and effective means to control the disease. Chinese wheat landrace Wangshuibai is an important resistant source from southern China. Several resistance QTLs in Wangshuibai were identified and mapped on chromosomes or chromosomal arms including 3BS, 4B, 6BS, 7AL, etc. In the present research, a mutant with increased FHB susceptibility, designated as NAUH117, was identified from the M(1) progenies of Wangshuibai irradiated by fast neutron. Genetic analysis of the F (1), F (2), and F (2:3) families from the reciprocal cross of Wangshuibai and NAUH117 indicated that NAUH117 was a recessive mutant. Genome-wide molecular marker analysis identified a deletion in the short arm of chromosome 3B of NAUH117, spanning the region of FL0.57 to FL1.00 that covers the locus of Fhb1 previously mapped on chromosome 3BS. Further molecular cytogenetics characterization by bi-color fluorescence in situ hybridization using three repetitive sequences, pSc119.2, pAs1 and GAA-satellite indicated that a multiple chromosome rearrangements occurred in chromosomes 3B, 6B, 3D, 4D, and 3A of the mutant. During these processes, a distal fragment of chromosome arm 3BS was eliminated, which is confirmed by molecular marker analysis. Four markers covered the deletion fragment were used for analysis of the F (2) population. The result showed that the 3BS deletion was only present in the susceptible plants, indicating that the deletion of 3BS fragment in NAUH117 increased susceptibility to FHB. The susceptible mutant will be valuable for the validation of the contribution of the resistant QTL located on 3BS, and for the characterization of the molecular mechanisms of FHB resistance in Wangshuibai.