Alterations on chloroplast ultrastructure and its function induced by Cassava common mosaic virus infection in cassava leaves

ANDREA A ZANINI; PABLO PACCIORETTI; DARIO F LUNA; MARIANELA S RODRIGUEZ; LILIANA DI FEO; AGOSTINA COLHAVINO

Simposio; 1st Brazilian Symposium on Photosynthesis: Perspectives to improve photosynthetic efficiency in a climate change scenario; 2020

Society for Experimental Biology

Cassava is one of the most widely grown tuber crops and an important food security crop. Its productivity is conditioned by the starch accumulation from CO2 fixation and the source-sink relationship. Cassava common mosaic virus (CsCMV) is a potexvirus that causes systemic infections in cassava plants, leading to foliar chlorotic mosaic with alternating light green/dark green and yellow patches and producing significant yield losses (30%-60%). To date, the physiological alterations and the mechanism underlying biotic stress during the CsCMV infection remains unknown. Our aim was to investigate the effects of CsCMV on chloroplast ultrastructure and its function. Immuno-electron microscopy from the middle part of CsCMV-infected leaves were evaluated. Furthermore, the relative chlorophyll content (SPAD), Chlorophyll-a fluorescence (ChlF) emission and net CO2 assimilation rates were measured. These parameters were assess on the fourth leaf (source leaf) in non-infected and CsCMV-infected plants, at three ontological stages: 60, 75 and 90 days after planting (DAP) and the net CO2 assimilation rates were measured at 90 and 210 DAP. Chloroplast ultrastructure alterations such us extrusion of the chloroplast membrane with amoeboid-shaped appearance, disorganized grana stacks and irregular arrangement of stroma lamellae were observed in infected mesophyll cells. These alterations were associated with an up to 35% reduction of SPAD and a decline of net CO2 assimilation rates (13.5% and 24.2% at 90 and 210 DAP, respectively). The effects of CsCMV infection on the performance index on absorption basis (PIabs) dropped up to 37%. Furthermore, the analysis of ChlF evidenced a progressive loss of both oxygen evolving complex activity (K band) and ?connectivity? within the tripartite system (core antenna-LHCII-Reaction Centre), L band. Our results suggest that CsCMV infection induces chloroplast distortion associated with progressive chloroplast function loss in source leaf tissue, leading to the loss of cassava tubers yield.