[Na-Sheng Lin] MiR398-regulated antioxidants contribute to Bamboo mosaic virus accumulation and symptom manifestationPOST:
Virus infections cause mosaic or mottling in leaves commonly accompanied by increased reactive oxygen species (ROS) levels as well. However, how ROS contributes to symptoms is less well documented. Bamboo mosaic virus (BaMV) causes chlorotic mosaic symptoms in both Brachypodium distachyon and Nicotiana benthamiana. The BaMV△CPN35 mutant with an N-terminal deletion of its coat protein gene exhibits asymptomatic infection independently of virus titer. The research team of Dr. Na-sheng Lin at Institute of plant and microbial biology found that H2O2 accumulated solely in BaMV-induced chlorotic spots by histochemical staining. Moreover, exogenous H2O2 treatment enhanced yellowish chlorosis in BaMV-infected leaves. Both BaMV and BaMV△CPN35 infection could induce the expression of Cu/Zu superoxide dismutase (CSD) antioxidants at mRNA and protein level. However, BaMV triggered the abundant accumulation of full-length NbCSD2 preprotein (prNbCSD2, without transit peptide cleavage), whereas BaMV△CPN35 induced a truncated prNbCSD2. Confocal microscopy showed that majority of NbCSD2-GFP predominantly localized in the cytosol upon BaMV infection, but BaMV△CPN35 infection tended to cause NbCSD2-GFP to remain in chloroplasts. By 5’ RLM-RACE, we validated CSDs are the targets of miR398 in vivo. Furthermore, BaMV infection increased the level of miR398, while the level of BaMV titer was regulated positively by miR398 but negatively by CSD2. In contrast, overexpression of cytosolic form NbCSD2, impairing the transport into chloroplasts, greatly enhanced BaMV accumulation. Taken together, our results indicate that induction of miR398 by BaMV infection may facilitate viral titer accumulation, and cytosolic prNbCSD2 induction may contribute to H2O2 accumulation, resulting in the development of BaMV chlorotic symptoms in plants.