Abundant, unusual RNAs on the leaf surface

It seems that there is no end to the surprises that RNA provides. To the old-school trio of mRNA, tRNA, and rRNA, the past 20 years have added miRNA, siRNA, tasiRNA and others, all with unique and specific roles in regulating gene activity. More recently, evidence has been accumulating that demonstrates non-cell autonomous RNA activities including as facilitators of plant defense. For example, in host-induced gene silencing, plants express a transgene encoding a double-stranded RNA that silences specific pathogen genes. Recent identification of abundant endogenously-produced extracellular RNAs (exRNAs) has led to several questions and hypotheses about their origin and function. Previous studies have looked at apoplastic RNAs (located between cells for example in cell walls) and RNAs encapsulated in extracellular vesicles (EVs). In this new work, Borniego and Singla-Rastogi et al. have characterized another pool of exRNAs, those abundant on the leaf surface but not encapsulated in vesicles. The authors carefully analyzed these RNAs and found that they are a unique population, distinct from those within the cell, within the apoplast, or within the EVs. The leaf surface RNAs are largely plant derived, mainly from tRNAs but other RNA classes are also represented. The authors speculate on their origin (maybe released from trichomes?) and suggest that they have a role in shaping the leaf microbiome. (Summary by Mary Williams @PlantTeaching.bksy.social @PlantTeaching)  Proc. Natl. Acad. Sci. USA 10.1073/pnas.2409090121