A homeodomain-leucine zipper I transcription factor, MeHDZ14,regulates internode elongation and leaf rolling in cassava(Manihot esculenta Crantz)

Drought stress impairs plant growth and other physiological functions. MeHDZ14, a homeodomainleucine zipper I transcription factor, is strongly induced by drought stress in various cassava cultivars.However, the role of MeHDZ14 in cassava growth regulation has remained unclear. Here we report that MeHDZ14 affected plant height, such that a dwarf phenotype and altered internode elongation were observed in transgenic cassava lines. MeHDZ14 was found to negatively regulate the biosynthesis of lignin. Its overexpression resulted in abaxially rolled leaves. The morphogenesis of leaf epidermal cells was inhibited by overexpression of MeHDZ14, with decreased auxin and gibberellin and increased cytokinin contents. MeHDZ14 was found to regulate many drought-responsive genes, including genes involved in cell wall synthesis and expansion. MeHDZ14 bound to the promoter of caffeic acid 3-Omethyltransferase 1(MeCOMT1), acting as a transcriptional repressor of genes involved in cell wall development. MeHDZ14 appears to act as a negative regulator of internode elongation and epidermal cell morphogenesis during cassava leaf development.

Down-regulation of MeMYB2 leads to anthocyanin accumulation and increases chilling tolerance in cassava(Manihot esculenta Crantz)

Chilling-induced accumulation of reactive oxygen species(ROS) is harmful to plants,which usually produce anthocyanins to scavenge ROS as protection from chilling stress.As a tropical crop,cassava is hypersensitive to chilling,but the biochemical basis of this hypersensitivity remains unclear.We previously generated Me MYB2-RNAi transgenic cassava with increased chilling tolerance.Here we report that Me MYB2-RNAi transgenic cassava accumulated less ROS but more cyanidin-3-O-glucoside than the wild type under early chilling stress.Under this stress,the anthocyanin biosynthesis pathway was more active in Me MYB2-RNAi lines than in the wild type,and several genes involved in the pathway,including Me TT8,were up-regulated by Me MYB2-RNAi in the transgenic cassava.Me MYB2 bound to the Me TT8 promoter and blocked its expression under both normal and chilling conditions,thereby inhibiting anthocyanin accumulation.Me TT8 was shown to bind to the promoter of Dihydroflavonol 4-reductase(Me DFR-2)and increased Me DFR-2 expression.Me MYB2 appears to act as an inhibitor of chilling-induced anthocyanin accumulation during the rapid response of cassava to chilling stress.

Selection and Identification of a Cellulase-producing Strain

[ Objective ] This study aimed to identify a cellulase-producing strain selected from tropical rain forestry soils. [ Method ] Morphologic observation and sequence analysis of 18S rDNA were conducted. [Result] A cellulase-preducing strain with high activity was obtained, and morphology of the strain was highly similar to that of Trichoderma reesei. Results of sequence analysis show that the 18S rDNA sequence shares 99% homology with Hypocreajecorina. [ Conclusion] The isolated cellulase-producing strain belongs to Trichoderma reesei.

Cell signaling during drought and/or cold stress in cassava

Cassava(Manihot esculenta Crantz)is a root crop significant in food security and various bio-industrial applications such as animal feed,modified starch,and biofuels.Drought and cold stress are two major factors limiting cassava production qualitatively and quantitatively,for which plants have evolved mechanisms to overcome the impact of these two stressors.In recent years,significant progress has been achieved in understanding the response mechanism of cassava plants to stress signals to tolerate the above stresses.In this review,core stress-signaling pathways,including transcription factor(TF)-related regulatory networks,plant hormone signaling,reactive oxygen species(ROS)scavenging,and non-coding RNA(ncRNA)and alternative splicing(AS)that modify gene expression levels in response to drought and/or cold stress in cassava,are summarized.Understanding these stress signaling and responses will increase our ability to improve the crops tolerance to multiple stresses for agricultural sustainability and food security for the growing world population.