Abstract
Laccases are encoded by a multigene family and widely distributed in plant genomes where they play roles oxidizing monolignols to produce higher-order lignin involved in plant development and stress responses. We identified 30 laccase genes (OsLACs) from rice, which can be divided into five subfamilies, mostly expressed during early development of the endosperm, growing roots, and stems. OsLACs can be induced by hormones, salt, drought, and heavy metals stresses. The expression level of OsLAC10 increased 1200-fold after treatment with 20 μM Cu for 12 h. The laccase activities of OsLAC10 were confirmed in an Escherichia coli expression system. Lignin accumulation increased in the roots of Arabidopsis over-expressing OsLAC10 (OsLAC10-OX) compared to wild-type controls. After growth on 1/2 Murashige and Skoog (MS) medium containing toxic levels of Cu for seven days, roots of the OsLAC10-OX lines were significantly longer than those of the wild type. Compared to control plants, the Cu concentration decreased significantly in roots of the OsLAC10-OX line under hydroponic conditions. These results provided insights into the evolutionary expansion and functional divergence of OsLAC family. In addition, OsLAC10 is likely involved in lignin biosynthesis, and reduces the uptake of Cu into roots required for Arabidopsis to develop tolerance to Cu.
Highlights
Laccase (EC 1.10.3.2) was originally found in Rhus vernicifera by Yoshida [1] and belongs to the ceruloplasmin oxidase family
Many studies have been conducted on fungal laccase, whereas studies on laccases in higher plants are limited and have considered disease resistance and lignin biosynthesis
Some laccase genes are expressed in non-woody tissues, and laccase participates in the oxidation of flavonoids, suggesting that laccase plays an important role in plant growth and defense responses [16,17]
Summary
Laccase (EC 1.10.3.2) was originally found in Rhus vernicifera by Yoshida [1] and belongs to the ceruloplasmin oxidase family. Some laccase genes are expressed in non-woody tissues, and laccase participates in the oxidation of flavonoids, suggesting that laccase plays an important role in plant growth and defense responses [16,17]. An important role of lignin biosynthesis in the response of plants to environmental stress has been reported and laccase may participate in the response to environmental stress by affecting lignin accumulation or its oxidative functions [22]. We found that Cu stress significantly enhanced laccase activity and lignin deposition in rice roots [33], and we speculated that laccase plays an important role in plant tolerance to Cu. In-depth molecular-level research is needed to better understand the function of rice laccase. Ectopic expression of OsLAC10 in Arabidopsis resulted in enhanced tolerance to Cu stress
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