A novel effector, CsSp1, from Bipolaris sorokiniana, is essential for colonization in wheat and is also involved in triggering host immunity

Abstract

The hemibiotrophic pathogen Bipolaris sorokiniana causes root rot, leaf blotching, and black embryos in wheat and barley worldwide, resulting in significant yield and quality reductions. However, the mechanism underlying the host-pathogen interactions between B. sorokiniana and wheat or barley remains unknown. The B. sorokiniana genome encodes a large number of uncharacterized putative effector proteins. In this study, we identified a putative secreted protein, CsSp1, with a classic N-terminal signal peptide, that is induced during early infection. A split-marker approach was used to knock out CsSP1 in the Lankao 9-3 strain. Compared with the wild type, the deletion mutant ∆Cssp1 displayed less radial growth on potato dextrose agar plates and produced fewer spores, and complementary transformation completely restored the phenotype of the deletion mutant to that of the wild type. The pathogenicity of the deletion mutant in wheat was attenuated even though appressoria still penetrated the host. Additionally, the infectious hyphae in the deletion mutant became swollen and exhibited reduced growth in plant cells. The signal peptide of CsSp1 was functionally verified through a yeast YTK12 secretion system. Transient expression of CsSp1 in Nicotiana benthamiana inhibited lesion formation caused by Phytophthora capsici. Moreover, CsSp1 localized in the nucleus and cytoplasm of plant cells. In B. sorokiniana-infected wheat leaves, the salicylic acid-regulated genes TaPAL, TaPR1, and TaPR2 were down-regulated in the ∆Cssp1 strain compared with the wild-type strain under the same conditions. Therefore, CsSp1 is a virulence effector and is involved in triggering host immunity.

A Bursaphelenchus xylophilus Effector, BxSCD3, Suppresses Plant Defense and Contributes to Virulence

“…This result indicated that BxSCD3 is a translocated effector. A similar result was found in Bipolaris sorokiniana effector CsSp1, which triggered plant immunity in both the nucleus and the cytoplasm of N. benthamiana cells [ 32 ]. There was no NLS or other organelle localization signals in CsSp1, so the localization of CsSp1 was predicted to be influenced by the target protein, and CsSp1 target proteins are present in both the nucleus and the cytoplasm of plants [ 32 ].…”

“…A similar result was found in Bipolaris sorokiniana effector CsSp1, which triggered plant immunity in both the nucleus and the cytoplasm of N. benthamiana cells [ 32 ]. There was no NLS or other organelle localization signals in CsSp1, so the localization of CsSp1 was predicted to be influenced by the target protein, and CsSp1 target proteins are present in both the nucleus and the cytoplasm of plants [ 32 ]. Thus, the localization of BxSCD3 may also be influenced by the target protein, which may be also present in both the nucleus and the cytoplasm of plants.…”

Graphene Oxide Exhibits Antifungal Activity against Bipolaris sorokiniana In Vitro and In Vivo

“…B. sorokiniana Lankao 9-3 was provided by Dr. Shengli Ding’s laboratory from Henan Agricultural University, as previously described [ 38 ] and was preserved on potato dextrose agar (PDA) medium at 4 °C. The old strain was transferred to a fresh new medium every two months to avoid compromising the strain’s vitality.…”

“…B. sorokiniana spores were obtained as previously described [ 38 ]. The mycelia of B. sorokiniana were incubated on a PDA medium for 5 d at 28 °C under alternating light and dark conditions.…”

“…Bipolaris sorokiniana ( B. sorokiniana ) is generally considered a hemibiotrophic pathogen related to root rot, leaf blotching, and black embryos in wheat and barley, among other grass species [ 38 , 39 ]. B. sorokiniana is widely distributed worldwide, bringing immeasurable losses to the yield and quality of many cereal crops.…”