Timing seed germination under changing salinity: a key role of the ERECTA receptor-kinases

Abstract

Appropriate timing of seed germination is crucial for the survival and propagation of plants, and for crop yield, especially in environments prone to salinity or drought. Yet, how exactly seeds perceive changes in soil conditions and integrate them to trigger germination remains elusive, especially once non-dormant. Here we report that the Arabidopsis ERECTA (ER), ERECTA-LIKE1 (ERL1) and ERECTA-LIKE2 (ERL2) leucine-rich-repeat receptor-like kinases synergistically regulate germination and its sensitivity to salinity and osmotic stress. Loss of ER alone, or in combination with ERL1 and/or ERL2 slows down the initiation of germination and its progression to completion, or arrests it altogether until better conditions return. That function is maternally controlled via the embryo surrounding tissues, primarily the properties of the seed coat determined during seed development on the mother plant, that relate to both seed coat expansion and subsequent differentiation, particularly the formation of its mucilage. Salt-hypersensitive er, er erl1, er erl2 and triple mutant seeds also exhibit increased sensitivity to ABA during germination, and under salinity show an enhanced upregulation of the germination repressors and inducers of dormancy ABA-insensitive-3, ABA-insensitive-5, DELLA encoding RGL2 and Delay-Of-Germination-1. These findings reveal a novel role of the ERECTA kinases in the sensing of conditions at the seed surface and the integration of developmental and stress signalling pathways in seeds. They also open novel avenues for the genetic improvement of plant adaptation to harsh soils. Highlight The ERECTA family of receptor-kinases regulates seed germination under salinity, through mucilage-mediated sensing of conditions at the seed surface, and interaction with secondary dormancy mechanisms.