Microtubule‐associated IQD9 orchestrates cellulose patterning in seed mucilage

Abstract

Arabidopsis seeds release large capsules of mucilaginous polysaccharides, which are shaped by an intricate network of cellulosic microfibrils. Cellulose synthase complexes are guided by the microtubule cytoskeleton, but it is unclear which proteins mediate this process in the seed coat epidermis.Using reverse genetics, we identified IQ67 DOMAIN 9 (IQD9) and KINESIN LIGHT CHAIN-RELATED 1 (KLCR1) as two highly expressed genes during seed development and comprehensively characterized their roles in cell wall polysaccharide biosynthesis.Mutations in IQD9 as well as in KLCR1 lead to compact mucilage capsules with aberrant cellulose distribution, which can be rescued by transgene complementation. IQD9 physically interacts with KLCR1 and localizes to cortical microtubules (MTs) to maintain their organization in seed coat epidermal (SCE) cells. IQD9 as well as a previously identified TONNEAU1 (TON1) RECRUITING MOTIF 4 (TRM4) protein act to maintain cellulose synthase velocity.Our results demonstrate that IQD9, KLCR1 and TRM4 are MT-associated proteins that are required for seed mucilage architecture. This study provides the first direct evidence that members of the IQD, KLCR and TRM families have overlapping roles in cell wall biosynthesis. Therefore, SCE cells provide an attractive system to further decipher the complex genetic regulation of polarized cellulose deposition.

Microtubule Regulation in Plants: From Morphological Development to Stress Adaptation

“…The plant seed coat protects the embryo and transmits information regarding the external environment [ 151 ]. TRM4 and IQD9 maintain cortical MT organization to orchestrate cellulose patterning in Arabidopsis seed mucilage [ 152 , 153 ]. MTs are important for the development and diameter determination of cotton fiber [ 154 ], an extension of seed coat [ 155 ], as shown by a recent finding that GhMAP20L5 is involved in cotton fiber elongation by interacting with GhTUB13 [ 156 ].…”

Branched mannan and xyloglucan as a dynamic duo in plant cell walls

“…The effects of Indeed, GGM is more important for cellulose deposition than branched xylan ( Voiniciuc et al, 2015a , Yang et al, 2020 ), another hemicellulose present in mucilage, while XyG-deficient xxt1 xxt2 xxt5 triple mutant seeds have wild-type mucilage staining ( Voiniciuc et al, 2015a ). Even the loss of several microtubule-related proteins that guide cellulose synthase movement ( Yang et al, 2022 ) caused less severe cellulose defects than GGM-deficient seeds. Therefore, mannans (akin to XyG in tip-growing cells; Kim et al, 2020 ) have unique roles in some tissues ( Voiniciuc, 2022 ).…”

The microtubule-associated protein SlMAP70 interacts with SlIQD21 and regulates fruit shape formation in tomato

“…At the molecular level, SUN/IQDs are proposed to function as scaffolding proteins in cell signaling (Abel et al, 2013; Bürstenbinder et al, 2013). Arabidopsis IQDs have been reported to interact with various MAPs and MAP-related proteins, including the microtubule-severing enzyme KTN1 (Li et al, 2021), Kinesin Light Chain-Related proteins (KLCRs) (Bürstenbinder et al ., 2013; Liu et al, 2016; Yang et al, 2022; Zang et al ., 2021), Phragmoplast Orienting Kinesins (POKs) and Pleckstrin-Homology GTPase-Activating proteins (PHGAPs) (Kumari et al ., 2021) to regulate apical hook formation, cellulose deposition, cell morphogenesis, cell division-plane orientation and establishment, respectively. These observations support the idea that distinct classes of MAPs regulate cell anisotropic growth, division patterns, and overall organ shape via differential microtubule modulating activities.…”