Dpto. Biología Vegetal, Facultad de Farmacia, Universidad de Valencia, Av. Vicente Andrés Estellés s/n, 46100 Burjassot, Valencia, Spain.
J Plant Physiol. 2013 Sep 1;170(13):1194-201. doi: 10.1016/j.jplph.2013.03.015. Epub 2013 Apr 28.
Xyloglucan endotransglucosylase/hydrolase (XTHs: EC 2.4.1.207 and/or EC 3.2.1.151), a xyloglucan modifying enzyme, has been proposed to have a role during tomato and apple fruit ripening by loosening the cell wall. Since the ripening of climacteric fruits is controlled by endogenous ethylene biosynthesis, we wanted to study whether XET activity was ethylene-regulated, and if so, which specific genes encoding ripening-regulated XTH genes were indeed ethylene-regulated. XET specific activity in tomato and apple fruits was significantly increased by the ethylene treatment, as compared with the control fruits, suggesting an increase in the XTH gene expression induced by ethylene. The 25 SlXTH protein sequences of tomato and the 11 sequences MdXTH of apple were phylogenetically analyzed and grouped into three major clades. The SlXTHs genes with highest expression during ripening were SlXTH5 and SlXTH8 from Group III-B, and in apple MdXTH2, from Group II, and MdXTH10, and MdXTH11 from Group III-B. Ethylene was involved in the regulation of the expression of different SlXTH and MdXTH genes during ripening. In tomato fruit fifteen different SlXTH genes showed an increase in expression after ethylene treatment, and the SlXTHs that were ripening associated were also ethylene dependent, and belong to Group III-B (SlXTH5 and SlXTH8). In apple fruit, three MdXTH showed an increase in expression after the ethylene treatment and the only MdXTH that was ripening associated and ethylene dependent was MdXTH10 from Group III-B. The results indicate that XTH may play an important role in fruit ripening and a possible relationship between XTHs from Group III-B and fruit ripening, and ethylene regulation is suggested.
木葡聚糖内转葡糖苷酶/水解酶（XTHs：EC 2.4.1.207 和/或 EC 3.2.1.151）是一种木葡聚糖修饰酶，据推测它在番茄和苹果果实成熟过程中通过松解细胞壁发挥作用。由于呼吸跃变型果实的成熟受内源乙烯生物合成的控制，我们想研究 XET 活性是否受乙烯调控，以及如果是这样，哪些特定的编码成熟调控 XTH 基因实际上受乙烯调控。与对照果实相比，乙烯处理显著增加了番茄和苹果果实中的 XET 比活，表明乙烯诱导 XTH 基因表达增加。对番茄的 25 个 SlXTH 蛋白序列和苹果的 11 个 MdXTH 序列进行了系统进化分析，并分为三个主要分支。在成熟过程中表达最高的 SlXTHs 基因是来自第三组-B 的 SlXTH5 和 SlXTH8，在苹果中，第二组的 MdXTH2 和第三组-B 的 MdXTH10 和 MdXTH11。乙烯参与了成熟过程中不同 SlXTH 和 MdXTH 基因表达的调控。在番茄果实中，有 15 个不同的 SlXTH 基因在乙烯处理后表达增加，与成熟相关的 SlXTHs 也依赖于乙烯，属于第三组-B（SlXTH5 和 SlXTH8）。在苹果果实中，有 3 个 MdXTH 在乙烯处理后表达增加，唯一与成熟相关且依赖于乙烯的 MdXTH10 属于第三组-B。结果表明，XTH 可能在果实成熟过程中发挥重要作用，推测第三组-B 的 XTHs 与果实成熟和乙烯调控之间存在一定的关系。
