Abstract
In some legume–rhizobium symbioses, host specificity is influenced by rhizobial nodulation outer proteins (Nops). However, the genes encoding host proteins that interact with Nops remain unknown. We generated an Ensifer fredii HH103 NopP mutant (HH103ΩNopP), and analyzed the nodule number (NN) and nodule dry weight (NDW) of 10 soybean germplasms inoculated with the wild-type E. fredii HH103 or the mutant strain. An analysis of recombinant inbred lines (RILs) revealed the quantitative trait loci (QTLs) associated with NopP interactions. A soybean genomic region containing two overlapping QTLs was analyzed in greater detail. A transcriptome analysis and qRT-PCR assay were used to identify candidate genes encoding proteins that interact with NopP. In some germplasms, NopP positively and negatively affected the NN and NDW, while NopP had different effects on NN and NDW in other germplasms. The QTL region in chromosome 12 was further analyzed. The expression patterns of candidate genes Glyma.12g031200 and Glyma.12g073000 were determined by qRT-PCR, and were confirmed to be influenced by NopP.
Highlights
Soybean (Glycine max (L.) Merr.), which is an important protein source for humans and animals [1], establishes a symbiotic relationship with rhizobia in different soil environments [2]
When rhizobia (Bradyrhizobium and Ensifer species) symbiotically colonize soybean roots, the plants can fix atmospheric nitrogen in a process known as biological nitrogen fixation (BNF) [4], which is an efficient and environmentally friendly source of nitrogen
Three and four conditional QTLs were identified for nodule number (NN) and nodule dry weight (NDW), respectively, after inoculations with the wild-type E. fredii HH103 and NopP mutant strains (Table 2 and Figure 2)
Summary
Soybean (Glycine max (L.) Merr.), which is an important protein source for humans and animals [1], establishes a symbiotic relationship with rhizobia in different soil environments [2]. Previous studies revealed that E. fredii strains grow much faster than Bradyrhizobium species, and can nodulate at least 79 different genera of legumes (i.e., a very broad host range) [7,8]. E. fredii HH103 can nodulate many legumes, including soybean, which is considered its natural host plant [9]. The capacities of Ensifer fredii HH103 to grow faster than bradyrhizobia and nodulate soybean, make this strain valuable for understanding molecular mechanisms acting in the soybean-rhizobia interaction. Rhizobia can inject many effector proteins into host cells via type III, type IV, or type VI secretion systems The roles of these effectors are presumably similar to those of effectors from plant pathogens, which promote the infection process [20,21]. Howoweveevre,rQ, QinigndgoduouinioncouclualtaetdedwwithithHH1H0130h3ahsas aroauronudn5d05%0%momreorneondoudleuslethsathnaQniQngindgoduoiunoincuolcauteladtewditwhitHhHH1H031Ω03NΩoNpPo.pIPn. DInoDngonognnogn5g9549,4th, tehNe DNWDW incinrecarseeadseidn irnesrpesopnosensteo ttohethienfiencfteicotniobnybtyhethEe.Efr.efdrieidHii H1H0130Ω3NΩoNpoPpsPtrsatirna.inT.hTuhsu, sN, oNpoPppPopsoitsiviteivlyelaynadnd nengeagtiavteivlyelayffaefcfteecdtetdhethseysmybmiobtiioctircelraetliaotniosnhsiphsipbsebtweteweeneHn H1H0130a3nadnsdosyobyebaena,nw, iwthitthhtehdeifdfiefrfenrecnesceisnin thethseysmybmiobtiioctipchpehneontyoptyepseasmaomnognggegrmerpmlapslmassmins flinufelunecendcebdybtyhethiregirengentiectbicacbkagckroguronudns.ds. Je. gMaotli.vSecil.y20a1f8f,e1c9t,e3d43t8he symbiotic relationships between HH103 and soybean, with the differe4nocfe1s5in the symbiotic phenotypes among germplasms influenced by their genetic backgrounds
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