Tzafrir Iris, McElver John A, Liu Cm Chun-ming, Yang Li Jun, Wu Jia Qian, Martinez Audrey, Patton David A, Meinke David W
Department of Botany, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
Plant Physiol. 2002 Jan;128(1):38-51.
The titan mutants of Arabidopsis exhibit striking defects in seed development. The defining feature is the presence of abnormal endosperm with giant polyploid nuclei. Several TTN genes encode structural maintenance of chromosome proteins (condensins and cohesins) required for chromosome function at mitosis. Another TTN gene product (TTN5) is related to the ARL2 class of GTP-binding proteins. Here, we identify four additional TTN genes and present a general model for the titan phenotype. TTN1 was cloned after two tagged alleles were identified through a large-scale screen of T-DNA insertion lines. The predicted gene product is related to tubulin-folding cofactor D, which interacts with ARL2 in fission yeast (Schizosaccharomyces pombe) and humans to regulate tubulin dynamics. We propose that TTN5 and TTN1 function in a similar manner to regulate microtubule function in seed development. The titan phenotype can therefore result from disruption of chromosome dynamics (ttn3, ttn7, and ttn8) or microtubule function (ttn1 and ttn5). Three other genes have been identified that affect endosperm nuclear morphology. TTN4 and TTN9 appear to encode plant-specific proteins of unknown function. TTN6 is related to the isopeptidase T class of deubiquitinating enzymes that recycle polyubiquitin chains following protein degradation. Disruption of this gene may reduce the stability of the structural maintenance of chromosome complex. Further analysis of the TITAN network should help to elucidate the regulation of microtubule function and chromosome dynamics in seed development.
拟南芥的泰坦突变体在种子发育过程中表现出显著缺陷。其决定性特征是存在具有巨大多倍体细胞核的异常胚乳。几个TTN基因编码有丝分裂时染色体功能所需的染色体结构维持蛋白（凝聚素和黏连蛋白）。另一个TTN基因产物（TTN5）与GTP结合蛋白的ARL2类相关。在此，我们鉴定出另外四个TTN基因，并提出了泰坦表型的一般模型。通过对T-DNA插入系的大规模筛选鉴定出两个标签等位基因后，克隆了TTN1。预测的基因产物与微管蛋白折叠辅助因子D相关，微管蛋白折叠辅助因子D在裂殖酵母（粟酒裂殖酵母）和人类中与ARL2相互作用以调节微管蛋白动力学。我们提出TTN5和TTN1以类似方式发挥作用，在种子发育中调节微管功能。因此，泰坦表型可能是由于染色体动力学破坏（ttn3、ttn7和ttn8）或微管功能破坏（ttn1和ttn5）所致。已鉴定出另外三个影响胚乳核形态的基因。TTN4和TTN9似乎编码功能未知的植物特异性蛋白。TTN6与去泛素化酶的异肽酶T类相关，该类酶在蛋白质降解后回收多聚泛素链。该基因的破坏可能会降低染色体结构维持复合体的稳定性。对泰坦网络的进一步分析应有助于阐明种子发育中微管功能和染色体动力学的调控机制。
