ARF6 and ARF8 contribute to tissue reunion in incised Arabidopsis inflorescence stems

Previously, we found that auxin and wound-inducible hormones contributed to the control of tissue reunion in both the upper and lower parts of incised Arabidopsis stems by inducing the expression of ANAC071 and RAP2.6L, respectively. Here, we reveal how the expression of ANAC071 and RAP2.6L is controlled by auxin. An arf6 arf8 double mutant exhibited inhibition of cell division in pith tissue 1 week after incision; this was not true of either the single mutants or mutants in other ARF genes. ANAC071 and RAP2.6L expression was suppressed in incised stems of the arf6 arf8 mutant, but RAP2.6L expression was enhanced in non-incised stems. In addition, the expression of DEFECTIVE IN ANTHER DEHISCENCE1 (DAD1), which encodes a jasmonic acid biosynthetic enzyme, was induced by the incision in both wild-type and arf6 arf8 stems, but overall expression level was suppressed in the arf6 arf8 mutant. We thus propose that auxin accumulation promotes ANAC071 expression via ARF6 and ARF8 activity in the upper part of incised stems, and that a reduced auxin level induces RAP2.6L expression in the lower part of the incision as a result of its release from the suppression caused by the action of ARF6 and ARF8-mediated auxin in non-incised stems. Moreover, auxin signaling via ARF6 and ARF8 is essential for jasmonic acid production, via the induction of DAD1, to increase RAP2.6L expression during tissue reunion.