Cloning and sequence analysis of nine novel MYB genes in Taxodiaceae plants

Myeloblastosis （MYB） is one of the largest transcribed factor families in plants. To gain an overall picture of the evolution of MYB genes in relict plants, we cloned nine novel MYB genes in Taxodiaceae plants （ Taxodium distichum, Taxodium ascendens, Cryptomeria japonica var. Sinensis, Cryptomeria japonica cv. Araucarioides, Cryptomer Ja- ponica, Metasequoia glyptostroboides, Cunninghamia lanceolata, Tai- wania cryptomerioides and Glyptostrobus pensilis）. The deduced amino acid sequences for MYBs showed that the nine MYB proteins contained two DNA binding domains. The first domain is from amino acid position 29 to 78, wherein three tryptophanes at 33, 53 and 73 were separated by 19 amino acids, respectively. The second domain is from amino acid position 82 to 127, wherein three tryptophanes at 86, 105 and 124 were separated by 18 amino acids, respectively, whereas the first tryptophane at amino acid position 86 is replaced by a phenylalanine. The characteri- zation of these conserved domains at nine MYBs indicated that they all belong to the R2R3-MYB group. The secondary structure analysis showed that a-helix and 13-turn are the major motifs of the predicted secondary structure of MYBs. The three dimensional model of each MYB protein showed that the structure is like clip, making it more flexi- ble and mobile. The similarities between the nine MYB proteins in Taxodiaceae were calculated. The highest identical value of 99% is be- tween CjsMYB, CjMYB and CjaMYB, whereas the lowest value of 82% is between TaMYB and C1MYB. According to the phylogenetic tree, the distances between different genera were relatively large whereas those within genera were relatively small. As expected, accessions of the same genus formed a subgroup before being grouped with other genera.

Comparative physiological and transcriptomic analyses illuminate common mechanisms by which silicon alleviates cadmium and arsenic toxicity in rice seedlings

The inessential heavy metal/loids cadmium(Cd)and arsenic(As),which often co-occur in polluted paddy soils,are toxic to rice.Silicon(Si)treatment is known to reduce Cd and As toxicity in rice plants.To better understand the shared mechanisms by which Si alleviates Cd and As stress,rice seedlings were hydroponically exposed to Cd or As,then treated with Si.The addition of Si significantly ameliorated the inhibitory effects of Cd and As on rice seedling growth.Si supplementation decreased Cd and As translocation from roots to shoots,and significantly reduced Cd-and As-induced reactive oxygen species generation in rice seedlings.Transcriptomics analyses were conducted to elucidate molecular mechanisms underlying the Si-mediated response to Cd or As stress in rice.The expression patterns of the differentially expressed genes in Cd-or As-stressed rice roots with and without Si application were compared.The transcriptomes of the Cd-and As-stressed rice roots were similarly and profoundly reshaped by Si application,suggesting that Si may play a fundamental,active role in plant defense against heavy metal/loid stresses by modulating whole genome expression.We also identified two novel genes,0s01g0524500 and 0s06g0514800,encoding a myeloblastosis(MYB)transcription factor and a thionin,respectively,which may be candidate targets for Si to alleviate Cd and As stress in rice,as well as for the generation of Cd-and/or As-resistant plants.This study provides valuable resources for further clarification of the shared molecular mechanisms underlying the Si-mediated alleviation of Cd and As toxicity in rice.