Journal
PLANT AND CELL PHYSIOLOGY
Volume 55, Issue 4, Pages 801-810Publisher
OXFORD UNIV PRESS
DOI: 10.1093/pcp/pcu018
Keywords
Arabidopsis thaliana; Endoplasmic reticulum; Male gametogenesis; Molecular chaperone; Pollen tube
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Funding
- Ministry of Education, Culture, Sports, Science and Technology of Japan [1685101, 23120512, 25120711, 23570051, 19058005]
- Japan Science and Technology Agency [CREST]
- Grants-in-Aid for Scientific Research [22227003, 19058005, 23570051] Funding Source: KAKEN
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Immunoglobulin-binding protein (BiP) is a molecular chaperone of the heat shock protein 70 (Hsp70) family. BiP is localized in the endoplasmic reticulum (ER) and plays key roles in protein translocation, protein folding and quality control in the ER. The genomes of flowering plants contain multiple BiP genes. Arabidopsis thaliana has three BiP genes. BIP1 and BIP2 are ubiquitously expressed. BIP3 encodes a less well conserved BiP paralog, and it is expressed only under ER stress conditions in the majority of organs. Here, we report that all BiP genes are expressed and functional in pollen and pollen tubes. Although the bip1 bip2 double mutation does not affect pollen viability, the bip1 bip2 bip3 triple mutation is lethal in pollen. This result indicates that lethality of the bip1 bip2 double mutation is rescued by BiP3 expression. A decrease in the copy number of the ubiquitously expressed BiP genes correlates well with a decrease in pollen tube growth, which leads to reduced fitness of mutant pollen during fertilization. Because an increased protein secretion activity is expected to increase the protein folding demand in the ER, the multiple BiP genes probably cooperate with each other to ensure ER homeostasis in cells with active secretion such as rapidly growing pollen tubes.
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