Plant Hydathodes Detect Microbial Patterns to Close Hydathode Pores and Restrict Leaf Entry

Plants restrict microbial entry into their leaves by closing their stomata upon recognition of conserved microbe-associated molecular patterns (MAMPs). The hydathode pore is a stomata-like opening on leaf margins which are thought to lack MAMP recognition and to be an entry point for microbial pathogens. Here, we observe marginal hydathode pore closure in response to abscisic acid, and the MAMPs chitin and flg22 in Arabidopsis thaliana leaves. Hydathode pore closure occurs within 3-9 hours of chitin exposure and pores reopen after 12 hours. Under conditions when hydathode pores are open, external fluids enter approximately 80% of the marginal hydathodes within a leaf. After hydathode pores close in response to ABA, chitin or flg22, external fluids accumulate in under 20% of hydathodes with in a leaf. MAMP-induced hydathode restriction was similar for dye or fluorescent Pseudomonas syringae pv. tomato bacteria and was dependent on pattern recognition receptors including CERK1 for chitin and FLS2 for flg22. Chitin-induced hydathode limitation was also dependent on the NADPH oxidase RBOHF and was partially hampered in rbohD, lyk4 lyk5, bak1-5 bkk1, slac1-3 slah3-1 knockout mutants. Together, this work indicates that MAMP recognition regulates entry into the hydathode and induces transient closure of the hydathode pores.