Molecular cloning and expression analysis of mulberry MAPK gene family.

Mitogen-activated protein kinase (MAPK) cascades play an important role in regulating various biotic and abiotic stresses in plants. Although MAPKs have been identified and characterized in a few model plants, there is little information available for mulberry Morus sp. L., one of the most ecologically and economically important perennial trees. This study identified 47 mulberry Morus notabilis MAPK (MnMAPK) family genes: 32 MnMAPKKK, five MnMAPKK and ten MnMAPK genes, and cloned ten MnMAPK cDNA genes based on a genome-wide analysis of the morus genome database. Comparative analysis with MAPK gene families from other plants suggested that MnMAPKs could be divided into five subfamilies (groups A, B, C, D and E) and they could have similar functions in response to abiotic and biotic stresses. MnMAPK gene expression analysis of different stresses (high/low temperature, salt and drought) and signal molecules (ABA, SA, H2O2 and methyl jasmonate (MeJA)) revealed that all ten MnMAPK genes responded to high/low temperature, salt and drought stresses, and that nine of the ten MnMAPKs (MnMAPK7 excepted) could be induced by ABA, SA, H2O2 and MeJA, which suggested that MnMAPKs may play pivotal roles in signal transduction pathways. Our results indicated that almost all of the MnMAPKs may be involved in environmental stress and defense responses, which provides the basis for further characterization of the physiological functions of MnMAPKs.

Draft genome sequence of the mulberry tree Morus notabilis.

Human utilization of the mulberry-silkworm interaction started at least 5,000 years ago and greatly influenced world history through the Silk Road. Complementing the silkworm genome sequence, here we describe the genome of a mulberry species Morus notabilis. In the 330-Mb genome assembly, we identify 128 Mb of repetitive sequences and 29,338 genes, 60.8% of which are supported by transcriptome sequencing. Mulberry gene sequences appear to evolve ~3 times faster than other Rosales, perhaps facilitating the species' spread worldwide. The mulberry tree is among a few eudicots but several Rosales that have not preserved genome duplications in more than 100 million years; however, a neopolyploid series found in the mulberry tree and several others suggest that new duplications may confer benefits. Five predicted mulberry miRNAs are found in the haemolymph and silk glands of the silkworm, suggesting interactions at molecular levels in the plant-herbivore relationship. The identification and analyses of mulberry genes involved in diversifying selection, resistance and protease inhibitor expressed in the laticifers will accelerate the improvement of mulberry plants.