Centre of Pear Engineering Technology Research, State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing, 210095, China.
BMC Plant Biol. 2018 Feb 17;18(1):36. doi: 10.1186/s12870-018-1252-2.
The hydroxyproline-rich glycoprotein (HRGP) superfamily, comprising three families (arabinogalactan-proteins, AGPs; extensins, EXTs; proline-rich proteins, PRPs), is a class of proline-rich proteins that exhibit high diversity and are involved in many aspects of plant biology.
In this study, 838 HRGPs were identified from Chinese white pear (Pyrus bretschneideri) by searching for biased amino acid composition and conserved motifs. 405 HRGPs were derived from whole genome duplication (WGD) events which is suggested to be the major force of driving HRGPs expansion and the recent WGD event shared by apple and pear generated most duplicated HRGPs in pear. This duplication event drived the structural variation of the HRGPs encoding hydroxyproline (Hyp)-rich motifs. The rate of HRGPs evolution mainly impacted the Hyp-rich motifs even in chimeric HRGPs. During the evolution of 53 PRPs that are also typified by 7-deoxyloganetin glucosyltransferase-like genes, the duplication from PRP to non-PRP was indirectly modified by positive selection. These results suggested that the rate of HRGP evolution mainly influenced the Hyp-rich motifs even in chimeric HRGPs. The expression divergence of HRGPs was higher than that of other commonly duplicated genes. In pear pistil, 601 HRGPs exhibited expression, while in pear pollen, 285 HRGPs were expressed. The qPCR results revealed that Pbr036330.1 and Pbr010506.1 showed different expression profile in self-incompatibility of pear pistil.
The researches indicated that WGD events was the main duplication type during the evolution of HRGPs, and the highly variable Hyp-motifs might be accountable for the expansion, evolution and expression divergence of HRGPs and that this divergence may be responsible for the gain of new functions in plants.
富含羟脯氨酸的糖蛋白（HRGP）超家族由三个家族（阿拉伯半乳聚糖蛋白、AGPs；伸展蛋白、EXTs；富含脯氨酸的蛋白、PRPs）组成，是一类富含脯氨酸的蛋白质，具有高度的多样性，参与植物生物学的许多方面。
本研究通过搜索偏性氨基酸组成和保守基序，从中国白梨（Pyrus bretschneideri）中鉴定出 838 个 HRGPs。405 个 HRGPs 来源于全基因组复制（WGD）事件，这被认为是推动 HRGPs 扩张的主要力量，苹果和梨最近的 WGD 事件产生了梨中大多数重复的 HRGPs。这种复制事件驱动了 HRGPs 编码富含羟脯氨酸（Hyp）基序的结构变异。HRGPs 进化的速度主要影响富含 Hyp 的基序，即使在嵌合 HRGPs 中也是如此。在 53 个富含脯氨酸的蛋白（也以 7-去氧龙牙花素葡萄糖基转移酶样基因为特征）的进化过程中，PRP 向非 PRP 的复制是由正选择间接修饰的。这些结果表明，HRGP 进化的速度主要影响富含 Hyp 的基序，即使在嵌合 HRGPs 中也是如此。HRGPs 的表达分歧高于其他常见的重复基因。在梨雌蕊中，有 601 个 HRGPs 表达，而在梨花粉中，有 285 个 HRGPs 表达。qPCR 结果表明，Pbr036330.1 和 Pbr010506.1 在梨雌蕊自交不亲和中的表达模式不同。
研究表明，WGD 事件是 HRGPs 进化过程中的主要重复类型，高度可变的 Hyp 基序可能是 HRGPs 扩张、进化和表达分歧的原因，这种分歧可能是植物获得新功能的原因。
