PLANT U-BOX PROTEIN10 Regulates MYC2 Stability in Arabidopsis.

MYC2 is an important regulator for jasmonic acid (JA) signaling, but little is known about its posttranslational regulation. Here, we show that the MYC2 C-terminal region interacted with the PLANT U-BOX PROTEIN10 (PUB10) armadillo repeats in vitro. MYC2 was efficiently polyubiquitinated by PUB10 with UBC8 as an E2 enzyme and the conserved C249 in PUB10 was required for activity. The inactive PUB10(C249A) mutant protein retained its ability to heterodimerize with PUB10, thus blocking PUB10 E3 activity as a dominant-negative mutant. Both MYC2 and PUB10 were nucleus localized and coimmunoprecipitation experiments confirmed their interaction in vivo. Although unstable in the wild type, MYC2 stability was enhanced in pub10, suggesting destabilization by PUB10. Moreover, MYC2 half-life was shortened or prolonged by induced expression of PUB10 or the dominant-negative PUB10(C249A) mutant, respectively. Root growth of pub10 seedlings phenocopied 35S:MYC2 seedlings and was hypersensitive to methyl jasmonate, whereas 35S:PUB10 and jin1-9 (myc2) seedlings were hyposensitive. In addition, the root phenotype conferred by MYC2 overexpression in double transgenic plants was reversed or enhanced by induced expression of PUB10 or PUB10(C249A), respectively. Similar results were obtained with three other JA-regulated genes, TAT, JR2, and PDF1.2. Collectively, our results show that MYC2 is targeted by PUB10 for degradation during JA responses.