PdEPFL6 reduces stomatal density to improve drought tolerance in poplar

Abstract

Drought is an abiotic stress that affects growth, development and productivity of plants. Peptides play key roles in plant growth and development, acting in a similar manner as phytohormones. However, only a few peptides have been identified to play a role in abiotic stress tolerance of poplars. Here, we isolated an EPIDERMAL PATTERNING FACTOR (EPF) secreted Cys-rich small peptide PdEEPFL6 from NE19 [Populus nigra × (P. deltoides × P. nigra)] and explored its mechanism in plant response to drought stress. We found that PdEEPFL6 was greatly induced by dehydration treatment in poplar. To investigate its potential biological functions, PdEPFL6, was overexpressed in poplar 84 K (P. alba × P. glandulosa). PdEPFL6 overexpressing lines (OxPdEPFL6) significantly decreased stomatal density, resulting in the decrease of transpiration rate. OxPdEPFL6 lines maintained a higher photosynthetic rate and lower the water loss rate of leaves compared with the control, resulting in drought resistance increasing. Moreover, yeast two-hybrid and bimolecular fluorescence complementation assays revealed that PdEPFL6 interacted with PdTMM (receptor-like protein) and PdERECTA (receptor-like kinases). Overexpression of PdEPFL6 regulated the expression levels of MAPK-associated genes and significantly decreased the expressions of stomatal development-related transcription factors (PdSPCH and PdMUTE) under normal and drought conditions, leading to a decrease in stomatal density. Taken together, our findings show that PdEPFL6-PdERECTA/PdTMM module plays an essential role in stomatal development, the ligand-receptor pair plays an active role in regulating drought resistance by reducing stomatal density in poplar.