Abstract -The interaction of C-TERMINALLY ENCODED PEPTIDES (CEPs) with CEP RECEPTOR1 (CEPR1) controls root growth and development, as well as nitrate uptake, but has no known role in determining yield.

We used physiological, microscopic, molecular, and grafting approaches to demonstrate a reproductive tissue-specific role for CEPR1 in controlling yield and seed size. Independent Arabidopsis cepr1 null mutants showed disproportionately large reductions in yield and seed size relative to their decreased vegetative growth. These yield defects correlated with compromised reproductive development predominantly in female tissues, as well as chlorosis, and the accumulation of anthocyanins in cepr1 reproductive tissues.

Grafting and sink manipulation experiments demonstrated that CEPR1 acts locally in the reproductive bolt to control yield and seed size. Promoter-reporter analyses indicated CEPR1 expresses throughout the vasculature of reproductive organs, including in the “nutrient unloading domain” of the seed, but not in other seed tissues. This expression pattern implies that CEPR1 controls yield and seed size from the maternal tissue.

We demonstrated that transgenic CEPR1 rescued the yield and other phenotypes of cepr1. In addition, transcriptional analyses of cepr1 bolts showed alterations in the expression levels of several genes of the CEP-CEPR1 and nitrogen homeostasis pathways. This transcriptional profile was consistent with cepr1 bolts being nitrogen deficient and with a reproductive tissue-specific function for CEP-CEPR1 signalling.

Together, the results reveal a local role for CEPR1 in the maternal reproductive tissue in determining seed size and yield, likely via the control of nitrogen delivery to the reproductive sinks. Our data suggests that CEPR1 plays a broader role in controlling nitrogen homeostasis at the whole-plant level beyond roles previously identified in root nitrogen acquisition and root system architecture.

Biography - Michael is a PhD candidate in the Djordjevic lab, Division of Plant Sciences, RSB, ANU. Prior to his PhD, he completed a Bachelor of Science (Advanced) (Honours) at ANU.