The Soybean mosaic virus (SMV) coat protein (CP) is necessary for virion assembly and viral cell-to-cell and long-distance movements in plants. We previously showed that the C-terminal region of the SMV CP is required for CP self-interaction. In the present study, we generated SMV mutants containing CPs with single amino acid substitutions of the charged amino acids in the C-proximal region. Infectivity and cell-to-cell movement of the SMV mutants were examined in soybean plants. Through this genetic approach, we identified three charged amino acid residues (R245, H246, and D250) in the surface-exposed C-terminus of the SMV CP that are critical for virus cell-to-cell and long-distance movement. Our findings suggest that the identified charged amino acids in the surface-exposed C-terminus of SMV CP are critical for CP intersubunit interactions and thereby for cell-to-cell and long-distance movement and virion assembly.

Molecular and biological characteristics of an isolate of Cucumber mosaic virus (CMV) from Glycine soja (wild soybean), named as CMV-209, was examined in this study. Comparison of nucleotide sequences and phylogenetic analyses of CMV-209 with the other CMV strains revealed that CMV-209 belonged to CMV subgroup I. However, CMV-209 showed some genetic distance from the CMV strains assigned to subgroup IA or subgroup IB. Infectious full-genome cDNA clones of CMV-209 were generated under the control of the Cauliflower mosaic virus 35S promoter. Infectivity of the CMV-209 clones was evaluated in Nicotiana benthamiana and various legume species. Our assays revealed that CMV-209 could systemically infect Glycine soja (wild soybean) and Pisum sativum (pea) as well as N. benthamiana, but not the other legume species.

Histone ubiquitylation/deubiquitylation plays a major role in the epigenetic regulation of gene expression. In plants, OTLD1, a member of the ovarian tumor (OTU) deubiquitinase family, deubiquitylates histone 2B and represses the expression of genes involved in growth, cell expansion, and hormone signaling. OTLD1 lacks the intrinsic ability to bind DNA. How OTLD1, as well as most other known plant histone deubiquitinases, recognizes its target genes remains unknown. Here, we show that Arabidopsis transcription factor LSH10, a member of the ALOG protein family, interacts with OTLD1 in living plant cells. Loss-of-function LSH10 mutations relieve the OTLD1-promoted transcriptional repression of the target genes, resulting in their elevated expression, whereas recovery of the LSH10 function results in down-regulated transcription of the same genes. We show that LSH10 associates with the target gene chromatin as well as with DNA sequences in the promoter regions of the target genes. Furthermore, without LSH10, the degree of H2B monoubiquitylation in the target promoter chromatin increases. Hence, our data suggest that OTLD1-LSH10 acts as a co-repressor complex potentially representing a general mechanism for the specific function of plant histone deubiquitinases at their target chromatin.

Histone ubiquitylation/deubiquitylation plays a major role in the epigenetic regulation of gene expression. In plants, OTLD1, a member of the ovarian tumor (OTU) deubiquitinase family, deubiquitylates monoubiquitylated histone 2B and represses the expression of genes involved in growth, cell expansion, and hormone signaling. Like many other histone-modifying enzymes, OTLD1 lacks the intrinsic ability to bind DNA. How OTLD1, as well as most other known plant histone deubiquitinases, is recruited specifically to the promoters of its target genes remains unknown. Here, we show that Arabidopsis transcription factor LSH10, a member of the ALOG protein family, interacts with OTLD1 in living plant cells. Loss-of-function LSH10 mutations relieve the OTLD1-promoted transcriptional repression of the target genes, resulting in their elevated expression, whereas recovery of the LSH10 function results in down-regulated transcription of the same genes. We then show that LSH10 associates directly with the target gene chromatin as well as with the specific DNA sequence motifs in the promoter regions of the target genes. Furthermore, in the absence of LSH10, the degree of H2B monoubiquitylation in the target promoter chromatin increases. Hence, our data suggest that OTLD1-LSH10 acts as a co-repressor complex, in which LSH1 recruits OTLD1 to the target gene promoters, potentially representing a general mechanism for recruitment of plant histone deubiquitinases to the target chromatin.