Trehalose 6-phosphate (T6P), the intermediate of trehalose biosynthesis and a signaling molecule, affects crop yield via targeting sucrose allocation and utilization. As there have been no reports of T6P signaling affecting secondary metabolism in a crop plant, the rubber tree Hevea brasiliensis serves as an ideal model in this regard. Sucrose metabolism critically influences the productivity of natural rubber, a secondary metabolite of industrial importance. Here, we report on the characterization of the T6P synthase (TPS) gene family and the T6P/SNF1-related protein kinase1 (T6P/SnRK1) signaling components in Hevea laticifers under tapping (rubber harvesting), an agronomic manipulation that itself stimulates rubber production. A total of fourteen TPS genes were identified, among which a class II TPS gene, HbTPS5, seemed to have evolved with a function specialized in laticifers. T6P and trehalose increased when the trees were tapped, this being consistent with the observed enhanced activities of TPS and T6P phosphatase (TPP) and expression of an active TPS-encoding gene, HbTPS1. On the other hand, SnRK1 activities decreased, suggesting the inhibition of elevated T6P on SnRK1. Expression profiles of the SnRK1 marker genes coincided with elevated T6P and depressed SnRK1. Interestingly, HbTPS5 expression decreased significantly with the onset of tapping, suggesting a regulatory function in the T6P pathway associated with latex production in laticifers. In brief, transcriptional, enzymatic, and metabolic evidence supports the participation of T6P/SnRK1 signaling in rubber formation, thus providing a possible avenue to increasing the yield of a valuable secondary metabolite by targeting T6P in specific cells.

Latex flow in Hevea brasiliensis (the Para rubber tree), the sole commercial source of natural rubber (cis-1,4-polyisoprene, NR), renders it uniquely suited for the study of plant stress responses. Calcineurin B-like interacting protein kinases (CIPK) serving as calcium-sensor protein kinases react with calcineurin B-like proteins (CBL) to play crucial roles in hormone signaling transduction and response to abiotic stress in plant developmental processes. However, little is known about their functions in Hevea. In this study, a total of twelve CBL (HbCBL) and thirty CIPK (HbCIPK) genes were identified from the Hevea genome. Structure and phylogenetic analysis assigned these CIPKs to five groups and CBLs to four groups, and mapped onto fourteen of the eighteen Hevea chromosomes. RNA-seq and qPCR analysis showed that the expressions of HbCBL and HbCIPK genes varied in the seven Hevea tissues examined, i.e., latex (cytoplasm of rubber-producing laticifers), bark, leaf, root, seed, female flower, and male flower. The expressions of two HbCBL and sixteen HbCIPK genes showed upward trends during leaf development. Following ethylene yield stimulation and the latex tapping treatment, both practices invoking stress, the expression levels of most latex-expressed genes were significantly altered. Yeast two-hybrid test revealed interactions for multiple combinations of HbCBLs and HbCIPKs with substantial gene expression in latex or other Hevea tissues. However, all the HbCBL-HbCIPK complexes examined did not recruit HbSOS1 or AtSOS1 to form functional salt tolerance SOS pathway in yeast cells. Taken together, the results suggested a role of the Hevea CBL-CIPK network as a point of convergence for several different signaling pathways in growth, development, and stress responses in relation to latex production.