Cassava common mosaic virus infection causes alterations in chloroplast ultrastructure, function, and carbohydrate metabolism of cassava plants

Abstract

Cassava common mosaic virus (CsCMV) is a potexvirus that causes systemic infections in cassava plants, leading to chlorotic mosaic and producing significant yield losses. To date, the physiological alterations and the mechanism underlying biotic stress during the cassava-CsCMV compatible interaction remains unknown. In this study, we found that CsCMV infection adversely modified chloroplast structure and had functional effects on chloroplasts in source leaves during the course of viral infection. Extrusion of the chloroplast membrane with amoeboid-shaped appearance and disorganized grana stacks were observed in infected mesophyll cells. These alterations were associated with up to 35% reduction of relative chlorophyll content, and a decline of CO 2 fixation (13.5% and 24.2% at 90 and 210 days after planting, respectively). The effects of CsCMV infection on the performance index on absorption basis dropped up to 37%. The analysis of chlorophyll a fluorescence showed a progressive loss of both oxygen evolving complex activity and "connectivity" within the tripartite system (core antenna-LHCII-reaction centre). Here, we report the latter phenomenon for the first time in a viral infection. The oxidative stress process was observed in CsCMV-infected plants (20.8% reduction of antioxidant capacity with respect to noninfected plants). Other effects of the pathogen included reduction of starch and maltose content in source leaves, and a significant increase (24.7%) of the sucrose:starch ratio, which indicates an altered pattern of carbon allocation. Our results suggest that CsCMV induces chloroplast distortion associated with progressive chloroplast function loss and diversion of carbon flux in source leaf tissue, leading to the loss of cassava tuber yield.

Cassava common mosaic virus infection affects growth and yield components of cassava plants (Manihot esculenta) in Argentina

“…As a consequence, photosynthesis reducing power would decrease and, therefore, less biomass would accumulate. A recent survey of cassava plants grown in greenhouse pots reported an increase in the elongation rate of CsCMV‐infected plants that did not correspond to an increase in nodes and leaves over time (Zanini et al, 2021). Those results suggest that PH is more related to the genotype and planting density, which decreases the incident light quality, than to the depletion of photoassimilates due to viral infection.…”

“…In this study, these traits were significantly affected, with a relative loss of 30%, 44%, and 24%, respectively. Thus, from the earliest stages of plant development, CsCMV affects the host photosynthetic system through alterations of the chloroplast ultrastructure and, as a consequence, of the integrity of the photosystems, resulting in the appearance of symptoms (Zanini et al, 2021). In cassava plants, the number of roots is defined at the early developmental stages, when the efficient photosynthetic activity makes photoassimilates highly available (Hershey, 1991; Medina et al, 2017a).…”

“…The symptomatology associated with CCMD comprises a wide range of leaf symptoms, such as mosaic patterns alternating with normal green and patches of intense yellow, and marked leaf distortion mainly in the younger leaves (Zanini et al, 2018). In recent studies, we found that these symptoms caused by CsCMV infections induce chloroplast alterations associated with progressive chloroplast function loss and deviation of carbon flux in source leaf tissue (Zanini et al, 2021).…”

“…However, our results indicate that CsCMV infection does have negative effects on the quality of tuberous roots of plants of cv. CM3306-4, because it significantly reduced root diameter and length.According toZanini et al (2021), alterations caused by CsCMV on photosynthesis and the ultrastructure of chloroplasts would reduce root size due to a lower carbohydrate accumulation and, consequently, a lower weight of tuberous roots. In this work, the potential damage produced by the infection of CsCMV during three successive cropping seasons shows that FWTR is the most affected parameter.…”

Impact of Wheat Streak Mosaic Virus on Peroxisome Proliferation, Redox Reactions, and Resistance Responses in Wheat

“…Chlorophyll content in leaves can be used to assess the immune response [ 63 , 64 ] as viral infection commonly causes reduction of both photosynthetic activity and chlorophyll content [ 63 , 65 ]. Reduction of chlorophyll a and b occurs in sugar cane leaves infected with sugarcane yellow leaf virus [ 66 ], wheat infected with BYDV [ 67 ], and cassava infected with cassava common mosaic virus [ 68 ]. Higher chlorophyll content indicates stronger immunity.…”