AUTHOR=Jiang Hua , Li Kai , Gai Junyi 

TITLE=Optimizing RNAi-Target by Nicotiana benthamiana-Soybean Mosaic Virus System Drives Broad Resistance to Soybean Mosaic Virus in Soybean

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.739971

DOI=10.3389/fpls.2021.739971

ISSN=1664-462X

ABSTRACT=<p>Soybean mosaic virus (SMV) is a prevalent pathogen of soybean (<italic>Glycine max</italic>). Pyramiding multiple SMV-resistance genes into one individual is tedious and difficult, and even if successful, the obtained multiple resistance might be broken by pathogen mutation, while targeting viral genome <italic>via</italic> host-induced gene silencing (HIGS) has potential to explore broad-spectrum resistance (BSR) to SMV. We identified five conserved target fragments (CTFs) from <italic>S1</italic> to <italic>S5</italic> using multiple sequence alignment of 30 SMV genome sequences and assembled the corresponding target-inverted-repeat constructs (TIRs) from S1-TIR to S5-TIR. Since the inefficiency of soybean genetic transformation hinders the function verification of batch TIRs in SMV-resistance, the <italic>Nicotiana benthamiana-</italic>chimeric-SMV and <italic>N. benthamiana-</italic>pSMV-GUS pathosystems combined with <italic>Agrobacterium</italic>-mediated transient expression assays were invented and used to test the efficacy of these TIRs. From that, S1-TIR assembled from 462 bp CTF-<italic>S1</italic> with 92% conservation rate performed its best on inhibiting SMV multiplication. Accordingly, S1-TIR was transformed into SMV-susceptible soybean <italic>NN1138-2</italic>, the resistant-healthy transgenic T<sub>1</sub>-plants were then picked out <italic>via</italic> detached-leaf inoculation assay with the stock-plants continued for progeny reproduction (T<sub>1</sub> dual-utilization). All the four T<sub>3</sub> transgenic progenies showed immunity to all the inoculated 11 SMV strains under individual or mixed inoculation, achieving a strong BSR. Thus, optimizing target for HIGS <italic>via</italic> transient <italic>N. benthamiana-</italic>chimeric-SMV and <italic>N. benthamiana-</italic>pSMV-GUS assays is crucial to drive robust resistance to SMV in soybean and the transgenic S1-TIR-lines will be a potential breeding source for SMV control in field.</p>