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Jun 28
InterView with Dr. Maeli Melotto
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Aline Sartor Chicowski

Maeli Melotto

Aline Sartor Chicowski

Dr. Maeli Melotto is a professor and scientist at the University of California, Davis, where she has worked for the past nine years. Ever since she was an undergraduate in biology at São Paulo State University (UNESP), Brazil, Maeli knew she wanted to be a plant scientist. For her B.S. thesis, she surveyed biological nitrogen fixation efficiency in trees using a collection of native rhizobium isolates from local forests. From that moment on, she has studied plant–microbe interactions. First, she worked on cowpea and soybean associations with rhizobia for her M.S. degree at the University of São Paulo (USP), Brazil. For her Ph.D. thesis at Michigan State University (MSU), she worked on bean–Colletotrichum lindemuthianum interactions. Finally, during her postdoctoral training at the MSU-DOE Plant Research Laboratory, she worked on tomato and Arabidopsis interactions with the bacterium Pseudomonas syringae.

When she started her lab, first at the University of Texas in Arlington in 2008 and then at UC Davis in 2014, she expanded her research interests to study plant colonization by human bacterial pathogens. She chose to work with Escherichia coli O157:H7 and Salmonella enterica because they are the top microbial contaminants of freshly consumed foods in the United States and the world. Besides, "UC Davis is a perfect location to carry out projects focused on solving this problem that affects the national and international fresh produce market. Leafy greens production in California accounts for 70–80% of the national market, and multiple foodborne disease outbreaks have originated in the field," she explained.

Her main research goal is to uncover the mechanisms that allow these bacteria to survive and multiply in healthy leaves using lettuce and Arabidopsis as models. Even though these bacteria are not pathogenic on plants, lettuce and Arabidopsis serve as hosts for them and react to their presence. "At the molecular level, there are many similarities between Arabidopsis and lettuce responses to phytobacteria such as Pseudomonas syringae and these human pathogens," she explained. Her group discovered that some lettuce cultivars mount a strong immune response (pattern-triggered immunity, or PTI) against O157:H7 and S. enterica, but other cultivars allow for bacterial growth, posing a greater risk for the occurrence of foodborne illnesses.

For Dr. Melotto, one of the most important discoveries in plant immunity during the past few years was the work by Matsumura et al. (2022): "Mechanosensory Trichome Cells Evoke a Mechanical Stimulus-Induced Immune Response in Arabidopsis thaliana." This study explains the mechanosensory role of trichomes in Arabidopsis. Disease is the exception of all possible plant–microbe interactions, and many things happen on the leaf surface before a pathogen can internalize the leaf and damage internal tissues. "The leaf surface is an exposed, complex environment that plays a crucial role in protecting the plant from invaders. This work presented a fascinating story on how mechanical stimuli at the trichome triggers a wave of calcium signaling that triggers plant immunity systemically. It sounds like a danger-detecting antenna," she said.

Dr. Melotto's favorite paper is her first: "Development of a SCAR Marker Linked to the I Gene in Common Bean." This article was a product of her overcoming scientific barriers and a turning point in her career. "It marked a point in time when molecular marker-assisted selection to improve disease resistance was the state-of-the-art for crop breeding," she mentioned. The marker she developed is still useful to breeding programs focused on virus diseases. Her paper has been cited 239 times, including 2023 citations. "To me, that paper represents a molecular technology that made it to real applications towards developing genetically resistant, commercial cultivars of beans in many countries."

Her favorite part of her job as a professor and scientist is to study the literature to fully interpret data from her research. She loves to write discussions and review articles to create a big picture and think about the next steps in science. "The desire to be a scientist came naturally, and, to this day, I can't think of being anything else but a scientist," she said. Maeli points out that the hardest part of her work is that it lies in the intersection of three major disciplines: molecular plant–microbe interactions, food science, and agronomy, "which do not have a history of working together," she noted. "Our audience is highly diverse, and we must navigate through 'discipline-specific vocabularies' when communicating our science."

When talking about challenges in her career, Dr. Melotto mentioned that her first biggest obstacle was overcoming the English language barrier, as her native language is Portuguese. She mentioned that it took her a while to start thinking in English and stop translating everything in her mind before speaking, "a tiresome task that any non-native English speaker will understand." She also pointed out that the second biggest obstacle she had to overcome, and according to her "once in a while still is," is to cope with "impostor syndrome." Dr. Melotto advises someone starting their career to seek opportunities to ask questions of those they consider successful individuals and learn from their experiences. Maeli said she had excellent mentors who answered all the questions she had as they became relevant to each stage of her career. "I am very grateful to Dr. James D. Kelly, my Ph.D. advisor, and Dr. Sheng ​Yang He, my postdoctoral mentor, who guided me to be the best scientist I could be and helped me reach my potential," she proudly said.

Ten years from now, Dr. Melotto hopes to have trained great scientists and advanced the knowledge of how hormonal signaling drives plant immune responses at the cell and tissue levels. "I would like to uncover new regulatory nodes that connect plant growth and defense, which could be used for metabolic engineering toward crop resilience under biotic stresses," she explained.

When asked what being recognized as a Fellow of the American Association for the Advancement of Science (AAAS) means to her, she said, "I have never dreamt about receiving this honor. I am so very grateful to the anonymous person who nominated me. It still doesn't feel like I deserve it, but I am happy to share this recognition with my advisees who contributed to the discoveries and publications from our lab."​

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