How do plant viruses trick their hosts?

Viruses are obligate parasites and they need host cells for their replication

Viruses are biotrophs; to multiply they need a living host. Upon entrance into the host cells ꟷ they manipulate, subvert, and enhance local and systemic infection for own benefits. During multiplication, viruses are counter-attacked by their enemies in disguise with various weapons like physical and molecular. Despite having the well-equipped defense machinery, in some cases, host plants cannot prevent the viral infection and lead to disease development.

After successful infection, viral proteins hijack the host cellular proteins and operate them for their own multiplication. Disruption in these two biological processes (defense machinery and infection cycle) leads to compatible or incompatible host-viral interactions.

During co-evolution, viruses have developed the proteins that are capable of multiple functions because viruses’ genomes are smaller and encode only a few (3–10) proteins. These viral proteins also recruit host cellular proteins to accelerate viral replication.

The question is how viruses break down plant defense mechanisms to overcome barriers in their replication and recruit different host factors to reach this?

The answer is viruses tricked the host cellular organelles and impair their functions.

Chloroplast

The chloroplast is self-replicating organelles and abundantly present in plant cells. They carry out photosynthesis and generate ATP and NADPH ꟷ energy required to complete various cellular activities. Why do plant viruses break down the functions of chloroplast and how they do this?

The significance of chloroplast is the generation of reactive oxygen species (ROS), they are central players in defense mechanisms, resulting in programmed cell death (PCD) to prevent viral infection. Therefore, viruses break down the function of chloroplast to complete their motives which is replication.

Virus coat protein (CP) impairs the thylakoid membrane to inhibit the electron transport reaction in photosystem Ⅱ. This impairment caused the loss of energy production. Virus-chloroplast interactions are critical for the development of symptoms in plants. The virus changes chlorophyll structure reduces photosynthesis and reduction of chlorophyll.

Nucleus

In eukaryotes, the nucleus is the site of genetic material and strictly surveilled by nuclear core proteins (NCP) for protein in, out movements. Why do viruses need to interact with the host nucleus? However, viruses might cheat this regulation of nucleus-cytoplasmic pathways and access nuclear functions crucial for its replication.

“What is the password to get into the host cellular nucleus?”

Following are possible strategies to get into the nucleus

1. “Viruses can develop proteins with the signal sequence to the nucleus”

2. “They can develop proteins able to interact with nuclear host proteins”

The interaction between viral coat proteins and NCP is crucial for the entrance into the nucleus and use them for their own benefit.

Phases in Virus life cycle

There are four phases in the life cycle of viruses:

1. Transmission of virus particles

2. Infection

3. Virus multiplication

4. Sites of viral RNA and Viral protein synthesis