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The Hevea brasiliensis XIP aquaporin subfamily: Genomic, structural and functional characterizations with relevance to intensive latex harvesting

Lopez D., Ben Amira M., Brown D., Muries B., Brunel-Michac N., Bourgerie S., Porcheron B., Lemoine R., Chrestin H., Mollison E., Di Cola A., Frigerio L., Julien J.L., Gousset-Dupont A., Fumanal B., Label P., Pujade-Renaud V., Auguin D., Venisse J.S.. 2016. Plant Molecular Biology, 91 (4-5) : p. 375-396.

DOI: 10.1007/s11103-016-0462-y

X-Intrinsic Proteins (XIP) were recently identified in a narrow range of plants as a full clade within the aquaporins. These channels reportedly facilitate the transport of a wide range of hydrophobic solutes. The functional roles of XIP in planta remain poorly identified. In this study, we found three XIP genes (HbXIP1;1, HbXIP2;1 and HbXIP3;1) in the Hevea brasiliensis genome. Comprehensive bioinformatics, biochemical and structural analyses were used to acquire a better understanding of this AQP subfamily. Phylogenetic analysis revealed that HbXIPs clustered into two major groups, each distributed in a specific lineage of the order Malpighiales. Tissue-specific expression profiles showed that only HbXIP2;1 was expressed in all the vegetative tissues tested (leaves, stem, bark, xylem and latex), suggesting that HbXIP2;1 could take part in a wide range of cellular processes. This is particularly relevant to the rubber-producing laticiferous system, where this isoform was found to be up-regulated during tapping and ethylene treatments. Furthermore, the XIP transcriptional pattern is significantly correlated to latex production level. Structural comparison with SoPIP2;1 from Spinacia oleracea species provides new insights into the possible role of structural checkpoints by which HbXIP2;1 ensures glycerol transfer across the membrane. From these results, we discuss the physiological involvement of glycerol and HbXIP2;1 in water homeostasis and carbon stream of challenged laticifers. The characterization of HbXIP2;1 during rubber tree tapping lends new insights into molecular and physiological response processes of laticifer metabolism in the context of latex exploitation.

Mots-clés : hevea brasiliensis; latex; relation plante eau; génome; homéostasie; glycérol; phylogénie; saignée; côte d'ivoire

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