Xia Li

Complex biological processes such as plant growth and development are often under the control of transcription factors that regulate the expression of large sets of genes and activate subordinate transcription factors in a cascade-like fashion. Here, by screening candidate photosynthesis-related transcription factors in rice, we identified a DREB (Dehydration Responsive Element Binding) family member, OsDREB1C, in which expression is induced by both light and low nitrogen status. We show that OsDREB1C drives functionally diverse transcriptional programs determining photosynthetic capacity, nitrogen utilization, and flowering time. Field trials with OsDREB1C -overexpressing rice revealed yield increases of 41.3 to 68.3% and, in addition, shortened growth duration, improved nitrogen use efficiency, and promoted efficient resource allocation, thus providing a strategy toward achieving much-needed increases in agricultural productivity.

Induced resistance response is a potent and cost effective plant defense against pathogen attack. The effectiveness and underlying mechanisms of the suppressive ability by Bacillus cereus AR156 to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) in Arabidopsis has been investigated previously; however, the strength of induced systemic resistance (ISR) activity against Botrytis cinerea remains unknown. Here, we show that root-drench application of AR156 significantly reduces disease incidence through activation of ISR. This protection is accompanied with multilayered ISR defense response activated via enhanced accumulation of PR1 protein expression in a timely manner, hydrogen peroxide accumulation and callose deposition, which is significantly more intense in plants with both AR156 pretreatment and B. cinerea inoculation than that in plants with pathogen inoculation only. Moreover, AR156 can trigger ISR in sid2-2 and NahG mutants, but not in jar1, ein2 and npr1 mutant plants. Our results indicate that AR156-induced ISR depends on JA/ET-signaling pathway and NPR1, but not SA. Also, AR156-treated plants are able to rapidly activate MAPK signaling and FRK1/WRKY53 gene expression, both of which are involved in pathogen associated molecular pattern (PAMP)-triggered immunity (PTI). The results indicate that AR156 can induce SAR by the JA/ET-signaling pathways in an NPR1-dependent manner and involves multiple PTI components.

Although simultaneous drought and cold stress occurs, especially in northwestern and eastern regions of China, and is an important factor limiting agricultural productivity, there are few studies focusing on plant responses to a combination of drought and cold stress. Here, by partially overlapping drought and cold stresses, we characterized the acclimation of maize (Zea mays B73) to these two stresses using physiological measurements, as well as comparative transcriptomics combined with metabolomics and hormonal analyses during the stress treatments and recovery stages. The combined drought and cold stress and drought stress alone were accompanied by a decline in photosynthetic capacity and enhanced transcriptional response, and subsequent recovery of these following removal from stress, whereas cold stress alone was accompanied by irreversible damage to photosynthetic capacity and chloroplast structure. The stress combination induced transcription-associated metabolomic alterations, in which raffinose, trehalose-6-phosphate, and proline accumulated, and monosaccharide abundance increased. Concomitantly, the increased abscisic acid (ABA) content and upregulated ABA signaling pathway may have provided the transcriptional regulation for the metabolic changes. In a parallel experiment, ABA treatments prior to exposure of the plants to cold stress primed the plants to survive the cold stress, thus confirming a key role for the endogenous ABA activated by the drought pretreatment in acclimation of the plants to cold. We present a model showing that the plant response to the combined stress is multi-faceted and reveal an ABA-dependent maize acclimation mechanism to the stress combination.

Plant root architecture is highly plastic during development and can adapt to many environmental stresses. The proper distribution of roots within the soil under various conditions such as salinity, water deficit, and nutrient deficiency greatly affects plant survival. Salinity profoundly affects the root system architecture of Arabidopsis (Arabidopsis thaliana). However, despite the inhibitory effects of salinity on root length and the number of roots, very little is known concerning influence of salinity on root growth direction and the underlying mechanisms. Here we show that salt modulates root growth direction by reducing the gravity response. Exposure to salt stress causes rapid degradation of amyloplasts in root columella cells of Arabidopsis. The altered root growth direction in response to salt was found to be correlated with PIN-FORMED2 (PIN2) messenger RNA abundance and expression and localization of the protein. Furthermore, responsiveness to gravity of salt overly sensitive (sos) mutants is substantially reduced, indicating that salt-induced altered gravitropism of root growth is mediated by ion disequilibrium. Mutation of SOS genes also leads to reduced amyloplast degradation in root tip columella cells and the defects in PIN2 gene expression in response to salt stress. These results indicate that the SOS pathway may mediate the decrease of PIN2 messenger RNA in salinity-induced modification of gravitropic response in Arabidopsis roots. Our findings provide new insights into the development of a root system necessary for plant adaptation to high salinity and implicate an important role of the SOS signaling pathway in this process.

Heat and drought stress are projected to become major challenges to sustain rice (Oryza sativa L.) yields with global climate change. Both stresses lead to yield losses when they coincide with flowering. A significant knowledge gap exists in the mechanistic understanding of the responses of rice floral organs that determine reproductive success under stress. Our work connects the metabolomic and transcriptomic changes in anthers, pistils before pollination and pollinated pistils in a heat-tolerant (N22) and a heat-sensitive (Moroberekan) cultivar. Systematic analysis of the floral organs revealed contrasts in metabolic profiles across anthers and pistils. Constitutive metabolic markers were identified that can define reproductive success in rice under stress. Six out of nine candidate metabolites identified by intersection analysis of stressed anthers were differentially accumulated in N22 compared with Moroberekan under non-stress conditions. Sugar metabolism was identified to be the crucial metabolic and transcriptional component that differentiated floral organ tolerance or susceptibility to stress. While susceptible Moroberekan specifically showed high expression of the Carbon Starved Anthers (CSA) gene under combined heat and drought, tolerant N22 responded with high expression of genes encoding a sugar transporter (MST8) and a cell wall invertase (INV4) as markers of high sink strength.