title: Microautophagy involves programmed cell semi-death of sieve elements in developing caryopsis of Triticum aestivum L.
abstract: Differentiation of sieve elements (SEs) involves programmed cell semi-death, in which a small amount of organelles is retained. However, the mechanisms by which a large amount of SE cytoplasm is degraded and the specific proteases involved are not clear. In this study, we confirmed that the degradation of cytoplasm outside of the vacuole was mediated by microautophagy of the vacuole, and that the tonoplast selectively fused with the plasma membrane after most of the cytoplasm in the vacuoles was degraded. The integration of space enclosed a small amount of cytoplasm. Therefore, that fraction of the cytoplasm was preserved. At the same time, the cytosol was weakly acidic during membrane fusion because part of the tonoplast was ruptured. We also demonstrated that wheat aspartic protease (WAP1) and proteases including cathepsin B activity (PICA) were involved in programmed cell semi-death of SEs. PICA showed strongest activity before mass of the cytoplasm was degraded, which might contribute toward SE stability. We found that WAP1 mainly degraded the cytoplasm. Therefore, programmed cell semi-death of SEs might result from the joint action of vacuoles and multiple proteases.
authors.affiliation: Laboratory of Cell Biology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, China.
authors.forename: Wenli
authors.initials: W
authors.lastname: Yang
authors.affiliation: Laboratory of Cell Biology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, China.
authors.forename: Jingtong
authors.initials: J
authors.lastname: Cai
authors.affiliation: Laboratory of Cell Biology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, China.
authors.forename: Zhuqing
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: College of Plant Sciences and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, China.
authors.forename: Guangsheng
authors.initials: G
authors.lastname: Zhou
authors.affiliation: College of Plant Sciences and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, China.
authors.forename: Fangzhu
authors.initials: F
authors.lastname: Mei
authors.affiliation: Laboratory of Cell Biology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, China.
authors.forename: Likai
authors.initials: L
authors.lastname: Wang
mesh_terms: D001343:Autophagy / Q000502:physiology*; D016923:Cell Death / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D012639:Seeds / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D014908:Triticum / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D014617:Vacuoles / Q000502:physiology
keywords: SEs; WAP1; cytosolic acidification; microautophagy; programmed cell semi-death; proteases including cathepsin B activity