Pathogen Profile #17

Hello Robigalia Reader and welcome back to another week of Robigalia, delivering the latest in plant pathology directly to your inbox!

Today’s pathogen is utilised as a tool in plant molecular biology labs worldwide due to its ability to transfer part of its DNA into a host. Keep reading to learn more about this week’s pathogen. As a Robigalia subscriber, you also gain access to my online database and today’s title song!

Agrobacterium tumefaciens a bacterium commonly found in soil. It is best known for its ability to cause crown gall disease, a condition characterised by the formation of tumour-like growths, or galls, on the stems and roots of a wide range of plants, including fruit trees, grapevines, and ornamental plants. Crown gall disease was first described in Italy in 1897 on grapevine by Italian botanist Fridiano Cavara. The bacterium was later formally identified by Townsend and Smith in 1907, who named it Bacterium tumefaciens.

Many bacterial cells have plasmids, which are small, circular pieces of DNA that exist separately from the main bacterial chromosome. Plasmids can be shared between bacteria, allowing them to acquire and exchange beneficial genes. In the case of A. tumefaciens, it contains a tumour-inducing plasmid (Ti) that is transferred into plant cells during infection. This DNA integration causes the plant cells to produce opines, which serve as nutrients for the bacterium, leading to the formation of galls. The galls disrupt the plant's vascular system, limiting the flow of water and nutrients.

Limiting crown gall disease is challenging due to the bacterium's ability to survive in soil for extended periods, and unfortunately, there is no cure once a plant is infected. However, the preventative application of A. radiobacter strain K84 and the genetically modified strain K1026 is highly effective against pathogenic A. tumefaciens strains that produce the opines nopaline and succinamopine. While A. tumefaciens rarely causes plant death in mature plants, crown gall disease reduces yield by decreasing both fruit size and number. When seedlings or young cuttings are infected, stunted growth occurs, which is particularly problematic in nursery settings where plants are grown from seed or cuttings. Currently, management of the disease is limited to the destruction of infected stock

Beyond its role as a plant pathogen, A. tumefaciens has revolutionised plant molecular biology, particularly in genetic engineering. Scientists have harnessed its natural ability to transfer DNA into plant cells to create transgenic plants. By replacing the tumour-inducing genes with genes of interest, researchers can introduce new traits into plants, such as pest resistance or improved nutritional content. This method has become a cornerstone of modern agricultural biotechnology, enabling the development of genetically modified crops that are more resilient and productive. It is reported that over 70 plant species from 23 families have been engineered using these methods.

If you’re interested in diving into the science of Agrobacterium tumefaciens, I’ve summarised a few articles below. Robigalia subscribers can scroll down to access my online database, which includes full summaries of these and all other featured Robigalia articles.

Agrobacterium tumefaciens papers

Molecular characterization of stem gall disease caused by Agrobacterium tumefaciens (= Agrobacterium biovar 1) on Citrus trees as a new host, in the Eastern Mediterranean region of Turkey

• Stem gall disease caused by A. tumefaciens has been identified on citrus trees in Turkey's Eastern Mediterranean region, marking the first such report in the country. This bacterial disease, observed with low incidence in Hatay and Mersin provinces, poses a potential threat to citrus production.

Transmission and Management of Pathogenic Agrobacterium tumefaciens and Rhodococcus fascians in Select Ornamentals

• Pathogenic Agrobacterium tumefaciens and Rhodococcus fascians remain challenging in nursery settings. This study revealed the pathogens can be transmitted through contaminated pruning tools, posing a significant risk to ornamental plant nurseries. Despite testing various control products, none proved effective in preventing disease in real-world conditions, highlighting the critical importance of stringent sanitation practices to manage these bacterial threats.

Agrobacterium-mediated in planta transformation of horticultural plants: Current status and future prospects

• The article reviews the current advancements in Agrobacterium-mediated in planta transformation (AMIPT) methods for horticultural plants, emphasising the factors influencing transformation efficiency and discusses prospects for expanding AMIPT applications in plant breeding and genetic engineering.

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Until next week,

Alyssa