Abstract
Natural rubber latex production can be improved by ethylene stimulation in the rubber tree (Hevea brasiliensis). However, the expression levels of most functional proteins for natural rubber biosynthesis are not induced after ethylene application, indicating that post-translational modifications, especially protein phosphorylation, may play important roles in ethylene signaling in Hevea. Here, we performed a comprehensive investigation on evolution, ethylene-induced expression and protein–protein interaction of calcium-dependent protein kinases (CPKs), an important serine/threonine protein kinase family, in Hevea. Nine duplication events were determined in the 30 identified HbCPK genes. Expression profiling of HbCPKs in three rubber tree cultivars with low, medium and high ethylene sensitivity showed that HbCPK6, 17, 20, 22, 24, 28 and 30 are induced by ethylene in at least one cultivar. Evolution rate analysis suggested accelerated evolution rates in two paralogue pairs, HbCPK9/18 and HbCPK19/20. Analysis of proteomic data for rubber latex after ethylene treatment showed that seven HbCPK proteins could be detected, including six ethylene-induced ones. Protein–protein interaction analysis of the 493 different abundant proteins revealed that protein kinases, especially calcium-dependent protein kinases, possess most key nodes of the interaction network, indicating that protein kinase and protein phosphorylation play important roles in ethylene signaling in latex of Hevea. In summary, our data revealed the expression patterns of HbCPK family members and functional divergence of two HbCPK paralogue pairs, as well as the potential important roles of HbCPKs in ethylene-induced rubber production improvement in Hevea.
Highlights
Rubber tree (Hevea brasiliensis) is mainly cultivated in the tropical regions, providing the most production of natural rubber, an important industrial material [1]
Our work provides a more comprehensive investigation of the evolutionary relationships, expression patterns and protein–protein interaction (PPI) relationships of calcium-dependent protein kinases (CPKs) members in ethylene signaling in Hevea, as well as potential transgenic targets of molecular breeding of rubber tree for improving natural rubber production in the future
The expression levels of genes that known to involve in rubber biosynthesis are not upregulated upon ethylene stimulation
Summary
Rubber tree (Hevea brasiliensis) is mainly cultivated in the tropical regions, providing the most production of natural rubber, an important industrial material [1]. Despite the difficulty of molecular genetic research for rubber tree, many works have been performed to investigate important factors in ethylene-induced rubber production improvement (EIRP). Several physiological processes, such as sucrose transport [3], water uptake [4], and synthesis of defense proteins [5] are reported to be activated after ethylene stimulation in H. brasiliensis (termed as Hevea hereafter). Our work provides a more comprehensive investigation of the evolutionary relationships, expression patterns and PPI relationships of CPK members in ethylene signaling in Hevea, as well as potential transgenic targets of molecular breeding of rubber tree for improving natural rubber production in the future
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