ENB1 encodes a cellulose synthase 5 that directs synthesis of cell wall ingrowths in maize basal endosperm transfer cells

Development of the endosperm is strikingly different in monocots and dicots: it often manifests as a persistent tissue in the former and transient tissue in the latter. Little is known about the controlling mechanisms responsible for these different outcomes. Here we characterized a maize (Zea mays) mutant, endosperm breakdown1 (enb1), in which the typically persistent endosperm (PE) was drastically degraded during kernel development. ENB1 encodes a cellulose synthase 5 that is predominantly expressed in the basal endosperm transfer layer (BETL) of endosperm cells. Loss of ENB1 function caused a drastic reduction in formation of flange cell wall ingrowths (ingrowths) in BETL cells. Defective ingrowths impair nutrient uptake, leading to premature utilization of endosperm starch to nourish the embryo. Similarly, developing wild-type kernels cultured in vitro with a low level of sucrose manifested early endosperm breakdown. ENB1 expression is induced by sucrose via the BETL-specific Myb-Related Protein1 transcription factor. Overexpression of ENB1 enhanced development of flange ingrowths, facilitating sucrose transport into BETL cells and increasing kernel weight. The results demonstrated that ENB1 enhances sucrose supply to the endosperm and contributes to a PE in the kernel. Cell wall ingrowths of maize basal endosperm transfer layer cells are synthesized by a cellulose synthase complex containing ENB1 that enhances sucrose import, sustaining a persistent endosperm.

Automated summary

Development of the endosperm differs significantly between monocots and dicots, with persistent endosperm in monocots and transient endosperm in dicots. The mechanisms controlling these differences are not well understood. In this study, a maize mutant, enb1, was characterized, and it was found that the endosperm degradation was drastically increased during kernel development. The ENB1 gene was identified as a key regulator involved in cellulose synthesis and nutrient uptake in the endosperm cells. Additionally, ENB1 expression was found to be induced by sucrose, and overexpression of ENB1 enhanced sucrose transport and contributed to the formation of a persistent endosperm in the kernel.