Fertilization-dependent phloem end gate regulates seed size
Xiaoyan Liu, Kohdai P. Nakajima, Prakash Babu Adhikari, Xiaoyan Wu, Shaowei Zhu, Kentaro Okada, Tomoko Kagenishi, Ken‐ichi Kurotani, Takashi Ishida, Masayoshi Nakamura, Yoshikatsu Sato, Yaichi Kawakatsu, Liyang Xie, Chen Huang, Jiale He, Ken Yokawa, Shinichiro Sawa, Tetsuya Higashiyama, Kent J. Bradford, Michitaka Notaguchi, Ryushiro D. Kasahara
Abstract
Seed formation is essential for plant propagation and food production. We present a novel mechanism for the regulation of seed size by a newly identified "gate" at the chalazal end of the ovule regulating nutrient transport into the developing seed. This gate is blocked by callose deposition in unfertilized mature ovules (closed state), but the callose is removed after central cell fertilization, allowing nutrient transport into the seed (open state). However, if fertilization fails, callose deposition persists, preventing transportation of nutrients from the funiculus. A mutant in an ovule-expressed β-1,3-glucanase gene (AtBG_ppap) showed incomplete callose degradation after fertilization and produced smaller seeds, apparently due to its partially closed state. By contrast, an AtBG_ppap overexpression line produced larger seeds due to continuous callose degradation, fully opening the gate for nutrient transport into the seed. The mechanism was also identified in rice, indicating that it potentially could be applied widely to angiosperms to increase seed size.