Iris yellow spot virus-induced chloroplast malformation results in male sterility.

Iris yellow spot virus (IYSV) is one of the most devastating viral pathogens, which causes high economic losses in the onion yield. Physiological and genetic changes are associated with the appearance of chlorotic symptom in the infected plants. IYSV-N gene sequence analysis revealed that it shared sequence identity of 99% with other Egyptian isolates, at both genomic and proteomic levels. In addition, N protein sequence with computational examination indicated many motifs involved and played different roles in the virus activity and its regulation and stability were detected. In the Differential Display-Polymerase Chain Reaction (DD-PCR) study, a highly up-regulated gene at 15 days post-biological IYSV inoculation (dpi) was selected for sequencing. Based on the sequencing results that showed the identified gene was coding for a chloroplast-related gene, degenerate specific primers were designed for Real-Time PCR analysis. A significant change in the transcription level of the chloroplast-related gene after 15 dpi suggested that some IYSV proteins interact and/or regulate with chloroplast proteins and this finding supports the DD-PCR results. At 20 dpi, the ultrathin sections showed that IYSV infection caused many dramatic chloroplasts malformations. The malformation appeared as chloroplast broken envelope with the presence of numerous spherical particles inside it and chloroplasts with long stromule. Our findings indicated that IYSV interrupts normal chloroplast functions, as a part of the onion defence response, however many crucial factors remain to be elucidated and further studies are needed at both biological and molecular levels.