Abstract
RSX1 is a pectate lyase (EC 4.2.2.2) that is required for the secondary plasmodesmata formation in the cell wall between companion cells (CC) and sieve elements (SE) in the source leaves of Arabidopsis thaliana. We herein described the enzymatic properties of RSX1, with reference to a crystallographic structure of the putative pectate lyase Jun a 1, a causative cedar pollen allergen. We found that a recombinant RSX1 protein with an N-terminal deletion exhibits pectate lyase activity toward the substrate polygalacturonate. The recombinant protein also exhibited a comparable enzyme activity toward low-esterified pectin and far less activity toward high-esterified pectin. Because pectin is highly methyl-esterified in the middle lamellar of cell walls, our results suggest that a pectin methylesterase should collaborate with RSX1 to make pits through the middle lamellar pectin for the secondary plasmodesmata formation.
