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.
摘要：
拟南芥种子释放粘质多糖的大胶囊，由复杂的纤维素微纤维网络形成。纤维素合酶复合物由微管细胞骨架引导，但目前尚不清楚哪些蛋白质在种皮表皮中介导这一过程。利用反向遗传学，我们确定了IQ67域9（IQD9）和KINESIN轻链相关1（KLCR1）是种子发育过程中的两个高表达基因，并全面表征了它们在细胞壁多糖生物合成中的作用。IQD9和KLCR1的突变导致纤维素分布异常的致密胶浆胶囊，可以通过转基因互补来拯救。IQD9与KLCR1物理相互作用，并定位于皮质微管（MT），以维持其在种皮表皮（SCE）细胞中的组织。IQD9以及先前鉴定的TONNEAU1（TON1）再生基序4（TRM4）蛋白起维持纤维素合酶速度的作用。我们的结果表明IQD9，KLCR1和TRM4是种子粘液结构所需的MT相关蛋白。这项研究提供了第一个直接证据，即IQD成员，KLCR和TRM家族在细胞壁生物合成中具有重叠的作用。因此,SCE细胞提供了一个有吸引力的系统，可以进一步破译极化纤维素沉积的复杂遗传调控。
