Beeckman Tom, Przemeck Gerhard K H, Stamatiou George, Lau Rachel, Terryn Nancy, De Rycke Riet, Inzé Dirk, Berleth Thomas
Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, B-9000 Gent, Belgium.
Plant Physiol. 2002 Dec;130(4):1883-93. doi: 10.1104/pp.102.010603.
The products of the cellulose synthase A (CESA) gene family are thought to function as isoforms of the cellulose synthase catalytic subunit, but for most CESA genes, the exact role in plant growth is still unknown. Assessing the function of individual CESA genes will require the identification of the null-mutant phenotypes and of the gene expression profiles for each gene. Here, we report that only four of 10 CESA genes, CESA1, CESA2, CESA3, and CESA9 are significantly expressed in the Arabidopsis embryo. We further identified two new mutations in the RADIALLY SWOLLEN1 (RSW1/CESA1) gene of Arabidopsis that obstruct organized growth in both shoot and root and interfere with cell division and cell expansion already in embryogenesis. One mutation is expected to completely abolish the enzymatic activity of RSW1(CESA1) because it eliminated one of three conserved Asp residues, which are considered essential for beta-glycosyltransferase activity. In this presumed null mutant, primary cell walls are still being formed, but are thin, highly undulated, and frequently interrupted. From the heart-stage onward, cell elongation in the embryo axis is severely impaired, and cell width is disproportionally increased. In the embryo, CESA1, CESA2, CESA3, and CESA9 are expressed in largely overlapping domains and may act cooperatively in higher order complexes. The embryonic phenotype of the presumed rsw1 null mutant indicates that the RSW1(CESA1) product has a critical, nonredundant function, but is nevertheless not strictly required for primary cell wall formation.
纤维素合酶A（CESA）基因家族的产物被认为是纤维素合酶催化亚基的同工型，但对于大多数CESA基因而言，其在植物生长中的具体作用仍不清楚。评估单个CESA基因的功能需要鉴定每个基因的无效突变体表型和基因表达谱。在此，我们报道在拟南芥胚胎中10个CESA基因中只有4个，即CESA1、CESA2、CESA3和CESA9有显著表达。我们进一步在拟南芥的径向肿胀1（RSW1/CESA1）基因中鉴定出两个新突变，这些突变阻碍了地上部和根部的有序生长，并在胚胎发生过程中就干扰细胞分裂和细胞扩张。其中一个突变预计会完全消除RSW1（CESA1）的酶活性，因为它消除了三个保守的天冬氨酸残基之一，这些残基被认为对β-糖基转移酶活性至关重要。在这个推测的无效突变体中，初生细胞壁仍在形成，但很薄，高度起伏，且经常中断。从心形期开始，胚胎轴中的细胞伸长严重受损，细胞宽度不成比例地增加。在胚胎中，CESA1、CESA2、CESA3和CESA9在很大程度上重叠的区域表达，并可能在更高阶的复合物中协同作用。推测的rsw1无效突变体的胚胎表型表明RSW1（CESA1）产物具有关键的、非冗余的功能，但对于初生细胞壁的形成并非严格必需。
