UDP-glucosyltransferase UGT84A2/BRT1 is required for Arabidopsis nonhost resistance to the Asian soybean rust pathogen Phakopsora pachyrhizi

Nonhost resistance (NHR) of plants to fungal pathogens comprises different defense layers. Epidermal penetration resistance of Arabidopsis to Phakopsora pachyrhizi requires functional PEN1, PEN2 and PEN3 genes, whereas post-invasion resistance in the mesophyll depends on the combined functionality of PEN2, PAD4 and SAG101. Other genetic components of Arabidopsis post-invasion mesophyll resistance remain elusive. We performed comparative transcriptional profiling of wild-type, pen2 and pen2 pad4 sag101 mutants after inoculation with P.pachyrhizi to identify a novel trait for mesophyll NHR. Quantitative reverse transcription-polymerase chain reaction (RT-qPCR) analysis and microscopic analysis confirmed the essential role of the candidate gene in mesophyll NHR. UDP-glucosyltransferase UGT84A2/bright trichomes 1 (BRT1) is a novel component of Arabidopsis mesophyll NHR to P.pachyrhizi. BRT1 is a putative cytoplasmic enzyme in phenylpropanoid metabolism. BRT1 is specifically induced in pen2 with post-invasion resistance to P.pachyrhizi. Silencing or mutation of BRT1 increased haustoria formation in pen2 mesophyll. Yet, the brt1 mutation did not affect NHR to P.pachyrhizi in wild-type plants. We assign a novel function to BRT1, which is important for post-invasion NHR of Arabidopsis to P.pachyrhizi. BRT1 might serve to confer durable resistance against P.pachyrhizi to soybean.