The sugar transporter (STP) gene family encodes monosaccharide transporters that contain 12 transmembrane domains and belong to the major facilitator superfamily. STP genes play critical roles in monosaccharide distribution and participate in diverse plant metabolic processes. To investigate the potential roles of STPs in cassava (Manihot esculenta) tuber root growth, genome-wide identification and expression and functional analyses of the STP gene family were performed in this study. A total of 20 MeSTP genes (MeSTP1–20) containing the Sugar_tr conserved motifs were identified from the cassava genome, which could be further classified into four distinct groups in the phylogenetic tree. The expression profiles of the MeSTP genes explored using RNA-seq data showed that most of the MeSTP genes exhibited tissue-specific expression, and 15 out of 20 MeSTP genes were mainly expressed in the early storage root of cassava. qRT-PCR analysis further confirmed that most of the MeSTPs displayed higher expression in roots after 30 and 40 days of growth, suggesting that these genes may be involved in the early growth of tuber roots. Although all the MeSTP proteins exhibited plasma membrane localization, variations in monosaccharide transport activity were found through a complementation analysis in a yeast (Saccharomyces cerevisiae) mutant, defective in monosaccharide uptake. Among them, MeSTP2, MeSTP15, and MeSTP19 were able to efficiently complement the uptake of five monosaccharides in the yeast mutant, while MeSTP3 and MeSTP16 only grew on medium containing galactose, suggesting that these two MeSTP proteins are transporters specific for galactose. This study provides significant insights into the potential functions of MeSTPs in early tuber root growth, which possibly involves the regulation of monosaccharide distribution.

Background: This study aimed to explore the active oxygen scavenging mechanism of Kandelia candel, in order to provide a theoretical basis for further analysis on the physiological mechanism of salt tolerance in mangrove plants. Different concentrations of NaCl solution (0, 150, 300 and 450 mmol/L) were used for salt stress treatments on Kandelia candel, physiological indicators in the root of Kandelia candel were measured in different processing time. Results: With the increase of salt concentrations and processing time, the contents of total proteins in the root of Kandelia candel were reduced; the CAT activity, SOD activity, ASA content and MDA content all had decreased with the increase of salt concentrations and shown a trend from ascent to descent with the increase of processing time, the peak of ASA and MDA contents were observed at 6 h, that of SOD activity was observed at 9 h and that of CAT activity was at 12 h; POD activity had shown an overall upward trend with the increase of salt concentrations and processing time, which reached the maximum at 24 h; the variations of these physiological indicators were more significant in high concentrations of NaCl solution (450 mmol/L). Conclusions: A certain salt concentration (<300 mmol/L) was required for the growth of Kandelia candel seedlings. At the early stage of high-salt stress, Kandelia candel can rapidly activate antioxidant defense system to resist the salt induced oxidative stress, thus reducing the damages of oxidative stress to plasma membrane, which might be an effective means for Kandelia candel to resist high salt stress.

Mitogen-activated protein kinases (MAPKs) play important roles in plant growth and development, plant abiotic stresses signalling pathway and plant–pathogen interactions. However, little is known about the roles of MAPKs in modulating plant growth and pathogen resistance. In this study, we found that OsMAPK12–1, an alternatively spliced form of BWMK1 in rice (Oryza sativa L.), was induced by various elicitors, such as jasmonic acid, salicylic acid, melatonin and bacterial pathogens. To further investigate the involvement of OsMAPK12–1 in plant growth and stress responses to bacterial pathogens, we constructed OsMAPK12–1 overexpression and knockdown (RNAi) transgenic rice lines. Interestingly, overexpressing OsMAP12–1 inhibited seed germination and seedling growth. Additionally, the OsMAP12-1-overexpression lines displayed enhanced disease resistance against Xanthomonas oryzae pv. oryzae PXO99 and Xanthomonas oryzae pv. oryzicola RS105, whereas the OsMAPK12-1-RNAi lines were more susceptible to these pathogens than wild type. These results suggest that OsMAPK12-1 plays a negative role in plant growth and positively modulates disease resistance against bacterial blight and streak in rice.

Cassava bacterial blight is the most destructive disease in cassava, causing a significant reduction in its production. The innate immunity response, which has a broad spectrum and a persistent effect, is the basal defence of plants in response to pathogens. Isolation and identification of innate immune-related genes in cassava will contribute to understanding the disease resistance mechanism. In Arabidopsis, the receptor-like cytoplasmic kinase (RLCK) AtBIK1 is known to be an important signal mediator in pathogen-associated molecular pattern-triggered immunity (PTI) response, forming a signal complex from various receptors including the flagellin receptor FLS2, the chitin receptor CERK1 and the receptor for bacterial EF-Tu EFR (Zhang et al. 2010). In the present study, we selected a candidate receptor-like cytoplasmic kinase gene, MeBIK1, from the cassava genome. MeBIK1 encodes a 409 amino acid polypeptide comprising a typical serine/threonine protein kinase domain, and is located on the cell membrane. MeBIK1 gene expression was significantly increased upon stimulation with flagellin (flg22) and peaked at 1 h. In vitro genetic complementation experiment showed that MeBIK1 complemented the reduced pathogen-associated molecular pattern-triggered immunity (PTI) response in Arabidopsis bik1 mutant. Arabidopsis MeBIK1 overexpression lines OX1 demonstrated a strong resistance to Xanthomonas axonopodis pv. manihotis HN01, whereas its sensitivity to Pseudomonas syringae pv. tomato DC3000 was enhanced. The peak level of reactive oxygen species (ROS) burst was reached in different Arabidopsis plants (bik1, OX1 and wild type) at 12 min after induction with flg22. However, the OX1 showed significantly higher ROS levels than the control and mutant, whereas the lowest level of ROS burst was found in the bik1 mutant. These results indicate that cassava MeBIK1 has a similar function as Arabidopsis AtBIK1 and improves disease resistance in transgenic Arabidopsis by regulating the PTI response.