TY - JOUR T1 - Unfolded protein-independent IRE1 activation contributes to multifaceted developmental processes in Arabidopsis JF - Life Science Alliance JO - Life Sci. Alliance DO - 10.26508/lsa.201900459 VL - 2 IS - 5 SP - e201900459 AU - Kei-ichiro Mishiba AU - Yuji Iwata AU - Tomofumi Mochizuki AU - Atsushi Matsumura AU - Nanami Nishioka AU - Rikako Hirata AU - Nozomu Koizumi Y1 - 2019/10/01 UR - https://www.life-science-alliance.org/content/2/5/e201900459.abstract N2 - In Arabidopsis, the IRE1A and IRE1B double mutant (ire1a/b) is unable to activate cytoplasmic splicing of bZIP60 mRNA and regulated IRE1-dependent decay under ER stress, whereas the mutant does not exhibit severe developmental defects under normal conditions. In this study, we focused on the Arabidopsis IRE1C gene, whose product lacks a sensor domain. We found that the ire1a/b/c triple mutant is lethal, and heterozygous IRE1C (ire1c/+) mutation in the ire1a/b mutants resulted in growth defects and reduction of the number of pollen grains. Genetic analysis revealed that IRE1C is required for male gametophyte development in the ire1a/b mutant background. Expression of a mutant form of IRE1B that lacks the luminal sensor domain (ΔLD) complemented a developmental defect in the male gametophyte in ire1a/b/c haplotype. In vivo, the ΔLD protein was activated by glycerol treatment that increases the composition of saturated lipid and was able to activate regulated IRE1-dependent decay but not bZIP60 splicing. These observations suggest that IRE1 contributes to plant development, especially male gametogenesis, using an alternative activation mechanism that bypasses the unfolded protein-sensing luminal domain. ER -