The Sclerotinia sclerotiorum-inducible promoter pBnGH17D7 in Brassica napus: isolation, characterization, and application in host-induced gene silencing.

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, is among the most devastating diseases in Brassica napus worldwide. Conventional breeding for SSR resistance in Brassica species is challenging due to the limited availability of resistant germplasm. Therefore, genetic engineering is an attractive approach for developing SSR-resistant Brassica crops. Compared with the constitutive promoter, an S. sclerotiorum-inducible promoter would avoid ectopic expression of defense genes that may cause plant growth deficits. In this study, we generated a S. sclerotiorum-inducible promoter. pBnGH17D7, from the promoter of B. napus glycosyl hydrolase 17 gene (pBnGH17). Specifically, 5'-deletion and promoter activity analyses in transgenic Arabidopsis thaliana plants defined a 189 bp region of pBnGH17 which was indispensable for S. sclerotiorum-induced response. Compared with pBnGH17, pBnGH17D7 showed a similar response upon S. sclerotiorum infection, but lower activity in plant tissues in the absence of S. sclerotiorum infection. Moreover, we revealed that the transcription factor BnTGA7 directly binds to the TGACG motif in pBnGH17D7 to activate BnGH17. Ultimately, pBnGH17D7 was exploited for engineering Sclerotinia-resistant B. napus via host-induced gene silencing. It induces high expression of siRNAs against the S. sclerotiorum pathogenic factor gene specifically during infection, leading to increased resistance.

Natural variation in BnaA07.MKK9 confers resistance to Sclerotinia stem rot in oilseed rape.

Sclerotinia stem rot (SSR), caused by the necrotrophic fungus Sclerotinia sclerotiorum, is one of the most devastating diseases for several major oil-producing crops. Despite its impact, the genetic basis of SSR resistance in plants remains poorly understood. Here, through a genome-wide association study, we identify a key gene, BnaA07. MKK9, that encodes a mitogen-activated protein kinase kinase that confers SSR resistance in oilseed rape. Our functional analyses reveal that BnaA07.MKK9 interacts with BnaC03.MPK3 and BnaC03.MPK6 and phosphorylates them at the TEY activation motif, triggering a signaling cascade that initiates biosynthesis of ethylene, camalexin, and indole glucosinolates, and promotes accumulation of H2O2 and the hypersensitive response, ultimately conferring resistance. Furthermore, variations in the coding sequence of BnaA07.MKK9 alter its kinase activity and improve SSR resistance by ~30% in cultivars carrying the advantageous haplotype. These findings enhance our understanding of SSR resistance and may help engineer novel diversity for future breeding of oilseed rape.

[Effects of returning maize straw into field on the Zn forms and their availability in a calcareous soil].

Maize straws were put into nylon mash bags and buried in a calcareous soil to study the effects of returning maize straw into field on the calcareous soil Zn forms and their availability. Compared with Zn fertilization, returning maize straw into field had little contribution to the soil total Zn content. Both Zn fertilization and straw returning increased the soil DTPA-Zn content significantly, and the increment was larger under Zn fertilization. As compared to that in low Zn concentration straw, the Zn released from high Zn concentration straw after returned into soil was more easily transformed into soil DTPA-Zn, with the transformation rate reached 49.0%. The transformation rate of soil DTPA-Zn had a trend of decreasing first and increasing then after straw returned into soil, but had little change under Zn fertilization. The soil exchangeable Zn (Ex-Zn), carbonate bound Zn (Carb-Zn), manganese oxide bound Zn (OxMn-Zn), tightly organic bound Zn (Sbo-Zn), and mineral Zn (Min-Zn) contents had no significant differences among the treatments, but the soil weakly organic bound Zn (Wbo-Zn) content was significantly higher under Zn fertilization, compared with the treatments control and straw addition alone. It was considered that the Zn in maize straw could be easily transformed into soil DTPA-Zn, though the Zn concentration in straw was rather low. Therefore, Zn fertilization combined with returning maize straw into filed could be an effective way to improve the Zn supply capacity of calcareous soil.