In higher plants, seed mass is an important to evolutionary fitness. In this context, seedling establishment positively correlates with seed mass under conditions of environmental stress. Thus, seed mass constitutes an important agricultural trait. Here, we show loss-of-function of YODA (YDA), a MAPKK Kinase, and decreased seed mass, which leads to susceptibility to drought. Furthermore, we demonstrate that yda disrupts sugar metabolisms but not the gaseous plant hormone, ethylene. Our data suggest that the transcription factor EIN3 (ETHYLENE-INSENSITIVE3), integral to both sugar and ethylene metabolisms, physically interacts with YDA. Further, ein3-1 mutants exhibited increased seed mass. Genetic analysis indicated that YDA and EIN3 were integral to a sugar-mediated metabolism cascade which regulates seed mass by maternally controlling embryo size. It is well established that ethylene metabolism leads to the suppression of drought tolerance by the EIN3 mediated inhibition of CBF1, a transcription factor required for the expression genes of abiotic stress. Our findings help guide the synthesis of a model predicting how sugar/ethylene metabolisms and environmental stress are integrated at EIN3 to control both the establishment of drought tolerance and the production of seed mass. Collectively, these insights into the molecular mechanism underpinning the regulation of plant seed size may aid prospective breeding or design strategies to increase crop yield.
Keywords: Arabidopsis; ETHYLENE-INSENSITIVE3 (EIN3); YODA (YDA); drought tolerance; ethylene and sugar metabolisms; seed mass.