Biochemical and Molecular Characterization of a Hydroxyjasmonate Sulfotransferase from Arabidopsis thaliana

Abstract

12-Hydroxyjasmonate, also known as tuberonic acid, was first isolated from Solanum tuberosum and was shown to have tuber-inducing properties. It is derived from the ubiquitously occurring jasmonic acid, an important signaling molecule mediating diverse developmental processes and plant defense responses. We report here that the gene AtST2a from Arabidopsis thaliana encodes a hydroxyjasmonate sulfotransferase. The recombinant AtST2a protein was found to exhibit strict specificity for 11-and 12-hydroxyjasmonate with K m values of 50 and 10 M, respectively. Furthermore, 12-hydroxyjasmonate and its sulfonated derivative are shown to be naturally occurring in A. thaliana. The exogenous application of methyljasmonate to A. thaliana plants led to increased levels of both metabolites, whereas treatment with 12-hydroxyjasmonate led to increased level of 12-hydroxyjasmonate sulfate without affecting the endogenous level of jasmonic acid. AtST2a expression was found to be induced following treatment with methyljasmonate and 12-hydroxyjasmonate. In contrast, the expression of the methyljasmonate-responsive gene Thi2.1, a marker gene in plant defense responses, is not induced upon treatment with 12-hydroxyjasmonate indicating the existence of independent signaling pathways responding to jasmonic acid and 12-hydroxyjasmonic acid. Taken together, the results suggest that the hydroxylation and sulfonation reactions might be components of a pathway that inactivates excess jasmonic acid in plants. Alternatively, the function of AtST2a might be to control the biological activity of 12-hydroxyjasmonic acid.

Cytochrome P450 CYP94B3 mediates catabolism and inactivation of the plant hormone jasmonoyl-L-isoleucine

“…The production of residual amounts of 12OH-JA-Ile in wounded cyp94b3 leaves supports the existence of a JA-Ile-12-hydroxylase that is distinct from CYP94B3. CYP94s may also be involved in the synthesis of 12OH-JA, which accumulates to relatively high levels in wounded leaves (11,13,15,16). Reduction in JA levels through conversion to 12OH-JA may provide an alternative pathway for limiting the production of bioactive JA-Ile (11,13,15), as could ω-hydroxylation of 12-oxo-phytodienoic acid or other JA precursors.…”

“…Recent work showing that JA-Ile acts more selectively in the nucleus than other jasmonate derivatives (33) raises the additional possibility that 12OH-JA-Ile does not partition effectively to the site of hormone perception in the nucleus. It is likely that CYP94B3-mediated inactivation of JA-Ile involves further enzymatic modification of 12OH-JA-Ile, for example by glucosylation, sulfation, or further oxidation of the 12-hydroxy group (11,13,16,19). Such modifications are expected to restrict entry or otherwise modulate the manner in which the pentenyl side chain fits into the hydrophobic binding pocket of COI1 (5).…”

“…Among the pathways implicated in catabolism of the hormone are conversion of JA and JA-Ile to their corresponding 12-hydroxy derivatives (12OH-JAs), 12OH-JA (also known as tuberonic acid) and 12OH-JA-Ile, respectively (11,(13)(14)(15). The 12OH-JAs can be further metabolized to sulfoand glucosyl derivatives that are largely inactive in promoting responses typically attributed to jasmonate (13,16,17). However, the ability 12OH-JAs to induce certain physiological responses, including tuber formation and leaf closing, raises the possibility that these compounds signal independently of the COI1-JAZ receptor system (17,18).…”

The Amidohydrolases IAR3 and ILL6 Contribute to Jasmonoyl-Isoleucine Hormone Turnover and Generate 12-Hydroxyjasmonic Acid Upon Wounding in Arabidopsis Leaves

“…TA, one of the products of amidohydrolase activity, is also known to undergo further metabolism via two competing routes (2), one leading to the TA glucoside (TA-Glc), the other yielding the sulfonated derivative 12-HSO 4 -JA (13,14). We therefore investigated if differential TA conversion could result in variable TA levels in the different mutant backgrounds.…”

“…For example, the JA metabolite 12OH-JA was first described in potato and Solanaceous species for its tuber-inducing activity, hence its trivial name tuberonic acid (TA) (12). More recently, TA and its sulfonated or glucosylated derivatives were found as commonly occurring metabolites of JA, particularly in the wound response (13,14), but the mode of formation of TA and biological activity of its derivatives are still largely unknown. TA formation has, however, been proposed as a partial switch-off in JA signaling (14).…”