UC Riverside

Plant endogenous small RNA pathways generate non-coding regulatory RNAs that regulate gene expression through target mRNA cleavage, translation inhibition or chromosomal modifications. Regulation of small RNAs and their targets during pathogen infection is tightly controlled to promote defensive mechanisms against disease progression. The oomycete pathogen, Phytophthora sojae is a principal infectious agent of soybean. To date, there is limited information on small RNAs that regulate defense responsive genes against P. sojae.

Infection response in plants is evidently regulated in part by small RNAs. High-throughput sequencing of small RNA libraries constructed from P. sojae-infected and mock-infected soybean roots and subsequent computational analysis revealed approximately 324 known soybean miRNAs and 109 potential novel soybean miRNAs that differentially accumulate between the P. sojae-infected and mock-infected samples. Of these, 8 conserved miRNAs and 2 novel miRNAs were verified by Northern blot analysis. Targets of the miRNAs displayed abundance changes respective to their complementary miRNA's levels.

The down-regulation of the conserved miR393 by target mimicry points to a positive regulatory role for miR393 during pathogen response. In addition, we noted the induction of miRNA-directed expression of phasiRNAs from multiple NB-LRR loci. These results indicate a pool of miRNAs specific in responding to P. sojae infection.

Our study identified multiple conserved and novel soybean miRNAs with potential defensive roles against P. sojae. Our data demonstrates that plant response to pathogen infection is complex and multi-layered. Further study of small RNAs involved in defense regulation may contribute to combating Phytophthora diseases.