Bromeliad Brocchinia reducta , a rare carnivorous monocot, is a holocarnivorous plant secreting its own digestive enzymes

Carnivorous bromeliad Brocchinia reducta is a rare carnivorous plant. As a monocot, it is the youngest and most distantly related to the remaining ∼800 dicot carnivorous plant species. Although considered carnivorous for more than 40 years, it is believed that it does not secrete digestive enzymes and relies on microorganism-mediated digestion. Here we investigated the digestive physiology of B. reducta by measuring enzyme activity and using LC-ESI-MS/MS in response to feeding. We found prey-induced pH regulation and digestive capacity with secreted hydrolytic enzymes (e.g., aspartic protease, type I and III chitinase, GDSL hydrolase) similar to those found in other carnivorous lineages. Although the enzyme activity is rather low and comparable to the members of the carnivorous Sarraceniaceae family, the active prey response and presence of secreted enzymes placed B. reducta among truly holocarnivorous plants. Our results showed that a nutrient-poor environment exerts the same selective pressures on even distantly related plants and, through the process of convergent evolution, leads to the co-option of the same proteins for digestive function.