You go walking in a glorious field of flowers, you take in a deep breath… and immediately the idyllic peace and tranquility is ruined by a sneeze attack. You, my friend, are allergic to plant sperm – also known as pollen. Plant scientists across the globe are continuously researching all aspects of our pretty floral friends and we had some questions. Who else should we ask but Dr James Walker?

Dr Walker is a postdoctoral fellow and undergraduate mentor from the Salk Institute for Biological Studies in San Diego, but he previously hailed from the United Kingdom where he did his PhD at the John Innes Centre, Norwich.

You used to work with plant sperm… can you explain like I am 5 what sperm cells in flowering plants are?

JW: It’s the classic story of the birds and the bees. Imagine flowers and bees playing a game where bees help flowers to share tiny packets called pollen. These pollen packets contain daddy’s tiny instructions inside sperm cells that mix with a mummy’s instructions in another flower. This mix makes seeds, which are baby plants waiting to grow. 

How do you get plants in the mood to collect sperm samples? 

JW: Some plants make swimming sperm like humans do (except they have two tails!), which corkscrew through water when it rains to fertilise the female eggs. 

The plants sense light quality during the day to know when to make sperm, so I use a far-red light bulb to mimic these conditions and create the right mood lighting. Then, I simply apply drops of water to the male sex organs to cause sperm release and then I collect the water in a tube, which takes up a single Wednesday afternoon.

In simple terms, what is methylation and why is it important in plants and eukaryotes? 

JW: DNA methylation is a chemical tag that is sometimes added to the Cs in DNA. It is often called the fifth letter: methyl-cytosine (mC). These tags can block certain parts of DNA and this stops RNA and proteins being produced. It’s vital because it helps determine which parts of the plant DNA are active or inactive during different growth stages, affecting how the plant develops and functions.

What is single-cell genomics and how does it contribute to plant science research? 

JW: When we crush up the leaf cells of a plant, we can look at the DNA methylation and see how it relates to RNA and protein. The problem is, it’s a mix of all the cells we crushed up – like blending fruit into a smoothie and seeing the pink of the strawberries and yet tasting banana! 

Single-cell genomics is a great new technique that lets us go directly to each cell and look at their methylation and RNA so that we know the direct effect of DNA methylation in each cell type, such as photosynthetic cells and leaf vein cells, so we can now see red and taste strawberry and see yellow and taste banana. It’s shown us that the DNA methylation patterns are much more dynamic than we used to think!

What are you currently researching? 

JW: I’m exploring new, unique patterns of DNA methylation across various stages of plant development. This research is uncovering surprising differences in how DNA methylation occurs, not only in well-studied plants but also in less familiar species, offering fresh insights into plant genetics.

Understanding how plant DNA is turned on and off brings us closer to controlling these genetic mechanisms ourselves. Techniques like CRISPR-Cas9 now allow us to direct DNA methylation to specific genes, enabling us to influence plant development for improved crop yields and adaptation to changing climates.

I aim [in the future] to characterise DNA methylation across a broader range of plants, including ferns and algae, to understand their evolutionary significance. From this I’m hoping to establish a set of rules that explain the role of methylation in plant biology and how methylation patterns are made.

How did you get into this career? 

JW: In school I loved puzzles – especially secret messages sent between me and my friends that I solved using a cypher. I was fascinated by Biology when I learned about the As, Gs, Cs, and Ts of DNA and how combinations of these letters also “code” for proteins that make all living things work. The many puzzles that this branched into have kept me busy ever since! 

I coupled this interest to plants after a brilliant teacher showed us how plants have adaptations to thrive in their environment, like curling their leaves to trap moisture in dry conditions. This teacher ran a gardening club after school and I was shocked how just some water, dirt, and tiny seeds could produce entire cucumbers, carrots, and cabbages, which we could then eat!

What has been your biggest achievement in your scientific career (so far)?

JW: I discovered a plant that uses a rare form of DNA methylation (4mC instead of the typical 5mC). It has previously only been seen in bacteria, but I found that the plant has adopted the bacterial gene, which then goes into overdrive in the sperm to methylate DNA more than has ever been seen before. We think this methylation helps to package the genetic material for sperm function, an exciting development that we’re preparing for publication!

Have you got any crazy lab stories? 

JW: During my undergraduate degree at university in my first lab, a colleague’s glass bottle containing alcohol that was being used for sterilisation smashed and caught fire from a nearby Bunsen burner! 

We succeeded in putting out the fire but it had melted some plastic on the bench and set off the fire alarm, so the whole building was temporarily evacuated. It was a cold English November evening and all the scientists huddled together outside kept asking what had happened. The lab switched to plastic bottles after that and there haven’t been any problems since!

What is your favorite plant? 

JW: My favourite plant is Ipheion uniflorum, the first plant I ever worked on when I was a student at Kew Gardens in London. 

It’s admired for its beautiful flowers that come in different colours, but it strangely smells like onion! I spent a year sequencing DNA from the different varieties to look at plant evolution, as its DNA often breaks apart and rearranges itself into new combinations. I still smile every time I see the flowers in someone’s garden.