Ecophysiology of Virus-Infected Plants: A Case Study of Eupatorium makinoi Infected by Geminivirus

Abstract

Plant viruses are prevalent in wild plants. However, few studies have been conducted on virus infection in natural plant communities. This paper describes a series of our studies on the Eupatorium makinoi-geminivirus system in order to consider the role of plant viruses in natural plant communities. Eupatorium makinoi is a short-lived perennial, which is widely distributed in Japan. Variegated E. makinoi plants caused by geminivirus infection are prevalent in the field. After a virus epidemic in a local E. makinoi population, the number of plants declined and, consequently, the local population nearly became extinct. Inferior performances of virus-infected plants were attributed to impaired photosynthesis. Photosynthetic rates of virus-infected leaves were especially lowered under low irradiance. This decrease was caused by a loss of chlorophyll (Chl) proteins, particularly light-harvesting chlorophyll a/b binding proteins associated with photosystem II (LHCII). The preferential loss of LHCII was caused by a decrease in the activity of Chl synthesis. These studies demonstrate that geminiviruses play an important role in determining fitness of E. makinoi plants and clarify the physiological mechanism of the decrease in fitness of virus-infected E. makinoi. Lowered fitness of E. makinoi by the infection would underlie the population dynamics observed in the field. Thus, virus infection is one of the most important biotic factors that affect various ecological and evolutionary phenomena in natural ecosystems.

Abbreviations

ALA: 5-aminolevulinate

Chl: chlorophyll

Chlase: chlorophyllase

CP: coat protein

F_m: maximum fluorescence induced by a saturating pulse after dark adaptation

F_m′: maximum fluorescence induced by a saturating pulse in the presence of actinic light

HL: high light

LA: leaf area

LAR: leaf area ratio (= LA/W)

LHCI: light-harvesting chlorophyll a/b binding proteins associated with photosystem I

LHCII: light-harvesting chlorophyll a/b binding proteins associated with photosystem II

LL: low light

ML: medium light

MP: movement protein

NAR: net assimilation rate (= [1/LA] × [dW/dt])

NPQ: nonphotochemical quenching

PaO: pheophorbide a oxygenase

P_max: light-saturated photosynthetic rate at ambient CO₂

PPFD: photosynthetic photon flux density

Pchlide: protochlorophyllide

PSI: photosystem I

PSII: photosystem II

RGR: relative growth rate (= [1/W] × [dW/dt])

RQH: Red Queen Hypothesis

W: plant dry mass

Key words

Eupatorium makinoi - geminivirus - growth - light - LHCII - photosynthesis - population dynamics

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