A research team from China’s Nanjing and Huaiyin Normal University has discovered how a single gene shapes tomato fruit size.
In particular they have explored how the floral meristem which orchestrates the formation of flowers and ultimately defines fruit size is controlled by the SIKNU gene. Their work has revealed that zinc finger protein SlKNU directly shuts down key stem cell genes -SlWUS and SlCLV3 – to halt floral meristem growth at the right moment. Through advanced genetic and molecular approaches, the team showed that SlKNU functions as a molecular brake, ensuring flowers mature correctly and fruits reach optimal size, offering new insights into yield control in Solanum lycopersicum.
Using CRISPR/Cas9 gene editing, the researchers generated SlKNU knockout mutants, and plants containing them exhibited enlarged floral meristems, an increased number of floral organs, and fruits with significantly more carpels and locules than wild-type plants, resulting in visibly larger tomatoes. Microscopic analysis confirmed that the floral meristem diameter in mutants was much wider, linking SlKNU loss to enhanced stem cell activity. Conversely, plants overexpressing SlKNU showed stunted growth and reduced meristem vigour, yet still formed normal carpels, suggesting a precise regulatory role rather than developmental inhibition. Subsequent molecular assays revealed the mechanism behind this effect.
“Our study reveals how SlKNU acts like a conductor in the orchestra of flower development, directing when stem cells should stop dividing to define the final fruit size,” said Professor Bo Sun, corresponding author of the study. “By directly repressing SlWUS, SlCLV3, and SlCLV1, SlKNU ensures that floral meristem activity ends at the right time. Understanding this genetic control offers powerful opportunities for improving fruit yield and quality not only in tomato but also in other economically important crops.”
In a related study published at the same time, the team confirmed that SlKNU also acts as a molecular brake that stops excessive meristem growth to define fruit size. “Our work shows that SlKNU [also] serves as the critical ‘off switch’ for floral stem cells, shaping the number of carpels and, consequently, the size of tomato fruits,” Professor Bo Sun continued. “By directly repressing SlWUS, SlCLV3, and SlCLV1, SlKNU orchestrates a delicate balance between growth and termination within the floral meristem. Understanding this molecular logic not only explains why some tomatoes grow bigger but also provides a new handle for precision breeding in crop improvement.”
