Abstract
Histone H2B protein is not only structurally important for chromosomal DNA packaging but is also involved in the regulation of gene expression, including the immune response of plants against pathogens. In this study, we show that the potato virus X (PVX) infection resulted in the reduced expression of H2B at both the mRNA and protein level in Nicotiana benthamiana. Tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) was then used to down-regulate the expression of H2B in N. benthamiana and tests showed that the titre of TRV was similar in these plants to that in control treated plants. When these H2B-silenced plants were inoculated with PVX, the virus spread more slowly through the plant and there was a lower titre of PVX compared to non-silenced plants. Abnormal leaf development and stem necrosis were observed in the H2B-silenced plants, which were alleviated in H2B-silenced NahG transgenic plants suggesting the involvement of salicylic acid (SA) in the production of these symptoms. Indeed, quantitative reverse transcription (qRT)-PCR and liquid chromatography tandem mass spectroscopy (LC-MS) results showed that endogenous SA is increased in H2B-silenced N. benthamiana. Thus, downregulation of H2B induced the accumulation of endogenous SA, which was correlated with stem necrosis and a decreased accumulation of PVX in N. benthamiana.
Highlights
Histones are nuclear proteins that are classified into five major protein groups: histones H2A, H2B, H3, and H4 are known as the core histones, while histones H1/H5 are known as the linker histones (Luger et al, 1997; Bellaïche and Grégoire, 2006)
At 6 days post-inoculation, viral infection symptoms appeared on upper, uninoculated leaves of the PVX infected plants but not on the mock control plants (Figure 1A), FIGURE 1 | Expression levels of Histone H2B (H2B) transcripts and proteins in potato virus X (PVX)-infected Nicotiana benthamiana. (A) PVX symptoms at 6 dpi in N. benthamiana and mock-inoculated plant. (B) PVX coat protein (CP) gene was detected by RT-PCR. (C) H2B proteins in PVX infected or healthy plants were detected by western blot using the H2B antibody
At 13 dpi, a quantitative reverse transcription (qRT)-PCR assay showed that the expression level of H2B mRNAs in systemic leaves of PVX infected plants had recovered to about 70% of that in mock plants (Supplementary Figure S1)
Summary
Histones are nuclear proteins that are classified into five major protein groups: histones H2A, H2B, H3, and H4 are known as the core histones, while histones H1/H5 are known as the linker histones (Luger et al, 1997; Bellaïche and Grégoire, 2006). The core histone octamers (two molecules of each protein) act as spools that package eukaryotic chromosomal DNA into structural units called nucleosomes. In addition to their role in organizing eukaryotic DNA, post-translationally modified H2B proteins can modulate the nucleosome/chromatin structure or DNA accessibility to affect the transcriptional pathways linked to embryonic development and cell differentiation (Zhang, 2003; Shilatifard, 2006; Fleming et al, 2008; Kyriss et al, 2010; Ríos-Uzeda and Wallace, 2014; Rønningen et al, 2015; Sadakierska-Chudy and Filip, 2015). The development and differentiation of Arabidopsis thaliana stem cells correlates with changes in histone H2B acetylation (Rosa et al, 2014). Disrupting tomato H2B mono-ubiquitination by silencing SIHUB1 and SIHUB2 increases susceptibility to Botrytis cinerea, which is related to the balance between salicylic acid (SA)- and jasmonic acid (JA)/ethylene (ET)-mediated signaling pathways (Zhang et al, 2015)
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