H b NIN 2, a cytosolic alkaline/neutral‐invertase, is responsible for sucrose catabolism in rubber‐producing laticifers of H evea brasiliensis (para rubber tree)

Summary In H evea brasiliensis , an alkaline/neutral invertase ( A / N ‐Inv) is responsible for sucrose catabolism in latex (essentially the cytoplasm of rubber‐producing laticifers, the source of natural rubber) and implicated in rubber yield. However, neither the gene encoding this enzyme nor its molecular and biochemical properties have been well documented. Three H evea A / N ‐Inv genes, namely H b NIN 1 , 2 and 3 , were first cloned and characterized in planta and in E scherichia coli . Cellular localizations of H b NIN 2 m RNA and protein were probed. From latex, active A / N ‐Inv proteins were purified, identified, and explored for enzymatic properties. H b NIN 2 was identified as the major A / N ‐Inv gene functioning in latex based on its functionality in E . coli , its latex‐predominant expression, the conspicuous localization of its m RNA and protein in the laticifers, and its expressional correlation with rubber yield. An active A / N ‐Inv protein was partially purified from latex, and determined as H b NIN 2. The enhancement of H b NIN 2 enzymatic activity by pyridoxal is peculiar to A / N ‐Invs in other plants. We conclude that H b NIN 2, a cytosolic A / N ‐Inv, is responsible for sucrose catabolism in rubber laticifers. The results contribute to the studies of sucrose catabolism in plants as a whole and natural rubber synthesis in particular.