Roles of JnRAP2.6-like from the Transition Zone of Black Walnut in Hormone Signaling

Zhonglian Huang,Keith Woeste,Richard Meilan,Peng Zhao,Jose Medina,Turgay Unver

doi:10.1371/journal.pone.0075857

Abstract

An EST sequence, designated JnRAP2-like, was isolated from tissue at the heartwood/sapwood transition zone (TZ) in black walnut (Juglans nigra L). The deduced amino acid sequence of JnRAP2-like protein consists of a single AP2-containing domain with significant similarity to conserved AP2/ERF DNA-binding domains in other species. Based on multiple sequence alignment, JnRAP2-like appears to be an ortholog of RAP2.6L (At5g13330), which encodes an ethylene response element binding protein in Arabidopsis thaliana. Real-time PCR revealed that the JnRAP2-like was expressed most abundantly in TZ of trees harvested in fall when compared with other xylem tissues harvested in the fall or summer. Independent transgenic lines over-expressing JnRAP2-like in Arabidopsis developed dramatic ethylene-related phenotypes when treated with 50 µM methyl jasmonate (MeJA). Taken together, these results indicated that JnRAP2-like may participate in the integration of ethylene and jasmonate signals in the xylem and other tissues. Given the role of ethylene in heartwood formation, it is possible JnRAP2-like expression in the transition zone is part of the signal transduction pathway leading to heartwood formation in black walnut.

Highlights

IntroductionBlack walnut (Juglans nigra L.) is one of the most valuable fine hardwood tree species in the Midwestern U.S because of the excellent qualities of its heartwood
Heartwood formation is an important factor determining wood quality [1]
Over the full amino acid sequence, JnRAP2-like shared 59% similarity with RAP2.6L (Related to AP2.6L, At5g13330), which is a member of the B-4 subgroup in the ERF family, but almost 100% identity within the AP2 domain (Figure 3B), evidence that JnRAP2-like is an ortholog of Arabidopsis RAP2.6L

Summary

Introduction

Black walnut (Juglans nigra L.) is one of the most valuable fine hardwood tree species in the Midwestern U.S because of the excellent qualities of its heartwood. Kato [21] showed a connection in Cucurbita maxima between wounding, ethylene, ACC oxidase and the induction of phenylalanine ammonia-lyase, the first enzyme in the phenylpropanoid pathway. Hudgins and Franceschi [22] demonstrated that methyl jasmonate was far more effective in the induction of phenolic defenses in conifer xylem than wounding. They showed that the differentiation of resinsecreting cells in conifer xylem after treatment with methyl jasmonate was mediated by ethylene, which was perceived in xylem parenchyma cells, the primary cellular location of ACC

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Results

Conclusion