In higher plants, hexokinase (HXK) is a crucial enzyme that phosphorylates glucose, because there is no evidence for the existence of glucokinase (GLK). In the rubber tree laticifers, the phosphorylation of glucose initiates glycolysis and pentose phosphate pathways, which provide energy and other compounds required for latex regeneration. However, the mechanism of how HXKs participate in the latex regeneration process in laticifers is currently unknown. In this study, four HXK cDNAs (HbHXK1-4) were isolated from the rubber tree (Hevea brasiliensis) and sequenced. Nucleotide-derived amino acid sequences revealed the presence of conserved amino acids that are required for catalytic activity and subcellular targeting. Among these genes, HbHXK2 and 4 were found to be the predominant isoforms in latex (cytoplasm of laticifers) when compared with others. Phylogenetic and subcellular localization analysis revealed that HbHXK2 was presumably targeted to the chloroplast and HbHXK4 to the mitochondria. Both HbHXK2 and 4 were confirmed to have catalytic activities towards glucose and fructose with a significantly higher affinity for glucose. In yield-stimulating experiments, HbHXK4 was strongly induced by tapping and ethephon treatments; whereas, HbHXK2 had the opposite expression pattern. The abundance of HbHXK4 transcripts was consistent with the observed catalytic activity and latex yield. Furthermore, in laticifers, HbHXK4 was more efficient in phosphorylating glucose compared with HbHXK2. Based on these results, it is concluded that HbHXK2 and 4 are the key enzymes for glucose metabolism during latex regeneration and may contribute to the productivity of H. brasiliensis (para rubber tree), especially HbHXK4.

在高等植物中，己糖激酶（HXK）是使葡萄糖磷酸化的关键酶，因为没有证据表明存在葡萄糖激酶（GLK）。在橡胶树胶乳植物中，葡萄糖的磷酸化引发糖酵解和戊糖磷酸途径，从而提供能量和胶乳再生所需的其他化合物。但是，目前尚不清楚HXKs如何参与胶乳细胞的乳胶再生过程。在这项研究中，四组HXK的cDNA（HbHXK1-4）从橡胶树（隔绝巴西橡胶树）中并测序。核苷酸衍生的氨基酸序列揭示了催化活性和亚细胞靶向所需的保守氨基酸的存在。在这些基因中，HbHXK2当与其他胶乳（乳胶质的细胞质）比较时，发现有3种和4种是主要的同工型。系统发育和亚细胞定位分析表明，HbHXK2可能靶向叶绿体，HbHXK4可能靶向线粒体。证实HbHXK2和4均具有对葡萄糖和果糖的催化活性，并且对葡萄糖具有显着更高的亲和力。在刺激产量的实验中，敲击和乙烯利处理强烈诱导了HbHXK4的产生。而HbHXK2具有相反的表达模式。HbHXK4的丰度转录本与观察到的催化活性和胶乳产率一致。此外，在乳杆菌中，与HbHXK2相比，HbHXK4在葡萄糖磷酸化方面更有效。根据这些结果，可以得出结论，HbHXK2和4是乳胶再生过程中葡萄糖代谢的关键酶，可能有助于巴西布鲁氏菌（橡胶树）的生产力，尤其是HbHXK4。