Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung 80424, Taiwan.
J Exp Bot. 2024 Jan 1;75(1):152-167. doi: 10.1093/jxb/erad380.
Extensins (EXTs), a class of hydroxyproline-rich glycoprotein with multiple Ser-Pro3-5 motifs, are known to play roles in cell wall reinforcement and environmental responses. EXTs with repetitive Tyr-X-Tyr (YXY) motifs for crosslinking are referred as crosslinking EXTs. Our comprehensive study spanned 194 algal and plant species, categorizing EXTs into seven subfamilies: classical extensins (EXT I and II), arabinogalactan-protein extensins (AGP-EXTs), proline-rich extensin-like receptor kinases (PERKs), leucine-rich repeat extensins (LRX I and II), formin homology (FH) domain-containing extensins (FH-EXTs), proline-rich, arabinogalactan proteins, conserved cysteines (PAC) domain-containing extensins (PAC I and II), and eight-cysteine motif (8CM)-containing extensins (8CM-EXTs). In the examined dataset, EXTs were detected ubiquitously in plants but infrequently in algae, except for one Coccomyxa and four Chlamydomonadales species. No crosslinking EXTs were found in Poales or certain Zingiberales species. Notably, the previously uncharacterized EXT II, PAC II, and liverwort-specific 8CM-EXTs were found to be crosslinking EXTs. EXT II, featuring repetitive YY motifs instead of the conventional YXY motif, was exclusively identified in Solanaceae. Furthermore, tandem genes encoding distinctive 8CM-EXTs specifically expressed in the germinating spores of Marchantia polymorpha. This updated classification of EXT types allows us to propose a plausible evolutionary history of EXT genes during the course of plant evolution.
伸展蛋白（EXTs）是一类富含羟脯氨酸的糖蛋白，具有多个 Ser-Pro3-5 基序，已知其在细胞壁强化和环境响应中发挥作用。具有重复 Tyr-X-Tyr（YXY）基序用于交联的 EXT 被称为交联 EXT。我们的综合研究涵盖了 194 种藻类和植物物种，将 EXT 分为七个亚科：经典伸展蛋白（EXT I 和 II）、阿拉伯半乳聚糖蛋白伸展蛋白（AGP-EXTs）、富含脯氨酸的伸展蛋白样受体激酶（PERKs）、富含亮氨酸的重复伸展蛋白（LRX I 和 II）、成纤维细胞同源（FH）结构域包含伸展蛋白（FH-EXTs）、富含脯氨酸的阿拉伯半乳聚糖蛋白、保守半胱氨酸（PAC）结构域包含伸展蛋白（PAC I 和 II）和 8 个半胱氨酸基序（8CM）包含伸展蛋白（8CM-EXTs）。在所检查的数据集，EXTs 在植物中普遍存在，但在藻类中很少见，除了一个 Coccomyxa 和四个 Chlamydomonadales 物种。在 Poales 或某些 Zingiberales 物种中没有发现交联 EXT。值得注意的是，以前未被表征的 EXT II、PAC II 和地钱特有的 8CM-EXTs 被发现是交联 EXT。EXT II 具有重复的 YY 基序而不是常规的 YXY 基序，仅在茄科中被鉴定。此外，串联基因编码独特的 8CM-EXTs，特异性表达在 Marchantia polymorpha 萌发的孢子中。这种对 EXT 类型的更新分类使我们能够提出 EXT 基因在植物进化过程中的合理进化历史。
