A Novel Chloroplast-Localized Pentatricopeptide Repeat Protein Involved in Splicing Affects Chloroplast Development and Abiotic Stress Response in Rice

Pentatricopeptide repeat （PPR） proteins comprise a large family in higher plants and modulate organellar gene expression by participating in various aspects of organellar RNA metabolism. In rice, the family contains 477 members, and the majority of their functions remain unclear. In this study, we isolated and characterized a rice mutant, white stripe leaf （wsl）, which displays chlorotic striations early in development. Map-based cloning revealed that WSL encodes a newly identified rice PPR protein which targets the chloroplasts. In wsl mutants, PEP-dependent plastid gene expression was significantly down-regulated, and plastid rRNAs and translation products accumulate to very low levels. Consistently with the observations, wsl shows a strong defect in the splicing of chloroplast transcript rpl2, resulting in aberrant transcript accumulation and its product reduction in the mutant. The wsl shows enhanced sensitivity to ABA, salinity, and sugar, and it accumulates more H2O2 than wild-type. These results suggest the reduced translation efficiency may affect the response of the mutant to abiotic stress.

Identification of novel cis-elements bound by BplMYB46 involved in abiotic stress responses and secondary wall deposition

Transcription factors （TFs） play vital roles in various biological processes by binding to cis-acting elements to control expressions of their target genes. The MYB TF BplMYB46, from Betula platyphylla, is involved in abiotic stress responses and secondary wall deposition. In the present study, we used a TF-centered yeast onehybrid technology （TF-centered YIH） to identify the cis- acting elements bound by BplMYB46. We screened a shortinsert random library and identified three cis-elements bound by BplMYB46： an E-box （CA（A/T/C）（A/G/C）TG） and two novel motifs, a TO-box （T（GIA）TCG（C/G）） and a GT-box （A（G/T）T（AIC）GT（T/G）C）. Chromatin immunoprecipitation （CHIP） and effector-reporter coexpression assays inNicotiana tabacum confirmed binding of BplMYB46 to the TC-box, GT-box, and E-box motifs in the promoters of the phenylalanine ammonia lyase （PAL）, peroxidase （POD）, and superoxide dismutase （SOD） genes, which function in abiotic stress tolerance and secondary wall biosynthesis. This finding improves our understanding of potential regulatory mechanisms in the response to abiotic stress and secondary wall deposition of BplMYB46 in B. platyphylla.

Knockdown of the atypical protein kinase genes GhABC1K2-A05 and GhABC1K12-A07 make cotton more sensitive to salt and PEG stress

Activity of bc1 complex kinase(ABC1K)is an atypical protein kinase(aPK)that plays a crucial role in plant mitochondrial and plastid stress responses,but little is known about the responses of ABC1Ks to stress in cotton(Gossypium spp.).Here,we identified 40 ABC1Ks in upland cotton(Gossypium hirsutum L.)and found that the Gh ABC1Ks were unevenly distributed across 17 chromosomes.The GhABC1K family members included 35 paralogous gene pairs and were expanded by segmental duplication.The GhABC1K promoter sequences contained diverse cis-acting regulatory elements relevant to hormone or stress responses.The qRT-PCR results revealed that most Gh ABC1Ks were upregulated by exposure to different stresses.Gh ABC1K2-A05 and Gh ABC1K12-A07 expression levels were upregulated by at least three stress treatments.These genes were further functionally characterized by virus-induced gene silencing(VIGS).Compared with the controls,the Gh ABC1K2-A05-and Gh ABC1K12-A07-silenced cotton lines exhibited higher malondialdehyde(MDA)contents,lower catalase(CAT),peroxidase(POD)and superoxide dismutase(SOD)activities and reduced chlorophyll and soluble sugar contents under NaCl and PEG stress.In addition,the expression levels of six stress marker genes(Gh DREB2A,Gh SOS1,Gh CIPK6,Gh SOS2,Gh WRKY33,and Gh RD29A)were significantly downregulated after stress in the Gh ABC1K2-A05-and Gh ABC1K12-A07-silenced lines.The results indicate that knockdown of Gh ABC1K2-A05 and Gh ABC1K12-A07 make cotton more sensitive to salt and PEG stress.These findings can provide valuable information for intensive studies of Gh ABC1Ks in the responses and resistance of cotton to abiotic stresses.

Expression Analysis of Aldo-Keto Reductase 1 (AKR1) in Foxtail Millet (Setaria italica L.) Subjected to Abiotic Stresses

Foxtail millet (Setaria italica L.) is a drought-tolerant millet crop of arid and semi-arid regions. Aldo-keto reductases (AKRs) are significant part of plant defence mechanism, having an ability to confer multiple stress tolerance. In this study, AKR1 gene expression was studied in roots and leaves of foxtail millet subjected to different regimes of PEG- and NaCl-stress for seven days. The quantitative Real-time PCR expression analysis in both root and leaves showed upregulation of AKR1 gene during PEG and salt stress. A close correlation exits between expression of AKR1 gene and the rate of lipid peroxidation along with the retardation of growth. Tissue-specific differences were found in the AKR1 gene expression to the stress intensities studied. The reduction in root and shoot growth under both stress conditions were dependent on stress severity. The level of lipid peroxidation as indicated by MDA formation was significantly increased in roots and leaves along with increased stress levels. Finally, these findings support the early responsive nature of AKR1 gene and seem to be associated at least in part with its ability to contribute in antioxidant defence related pathways which could provide a better protection against oxidative stress under stress conditions.

Future challenges in understanding ROS in plant responses to abiotic stress

Plants must cope with a variety of environmental stresses. Most types of abiotic stresses, such as drought, salinity, flooding, heat and cold stress, disrupt the metabolic balance of cells, resulting in the enhanced production of reactive oxygen species （ROS）. While being well-known as a toxic by-product, recent studies about ROS focus on their roles as signaling molecules.

Active DNA demethylation in plants:20 years of discovery and beyond

Maintaining proper DNA methylation levels in the genome requires active demethylation of DNA.However,removing the methyl group from a modified cytosine is chemically difficult and therefore,the underlying mechanism of demethylation had remained unclear for many years.The discovery of the first eukaryotic DNA demethylase,Arabidopsis thaliana REPRESSOR OF SILENCING 1(ROS1),led to elucidation of the 5-methylcytosine base excision repair mechanism of active DNA demethylation.In the 20 years since ROS1 was discovered,our understanding of this active DNA demethylation pathway,as well as its regulation and biological functions in plants,has greatly expanded.These exciting developments have laid the groundwork for further dissecting the regulatory mechanisms of active DNA demethylation,with potential applications in epigenome editing to facilitate crop breeding and gene therapy.

Perspectives of Using L-Tryptophan for Improving Productivity of Agricultural Crops: A Review

Plant growth regulators are biologically active signaling molecules that regulate a number of plant physiological processes. Auxin(indole-3-acetic acid) is an important plant growth regulator and is synthesized within plant tissues through L-tryptophan(L-TRP)-dependent and-independent pathways. It has been found that plants respond to exogenously applied L-TRP due to insufficient endogenous auxin biosynthesis. The exogenous application of L-TRP is highly significant for normal plant growth and development.L-tryptophan is applied through foliar spray, seed priming, and soil application. Soil-applied L-TRP is either directly taken up by plants or metabolized to auxin by soil microbiota and then absorbed by plant roots. Similarly, foliar spray and seed priming with L-TRP stimulates auxin synthesis within plants and improves the growth and productivity of agricultural crops. Furthermore, L-TRP contains approximately 14% nitrogen(N) in its composition, which is released upon its metabolism within a plant or in the rhizosphere and plays a role in enhancing crop productivity. This review deals with assessing crop responses under the exogenous application of L-TRP in normal and stressed environments, mode of action of L-TRP, advantages of using L-TRP over other auxin precursors, and role of the simultaneous use of L-TRP and auxin-producing microbes in improving the productivity of agricultural crops. To the best of our knowledge, this is the first review reporting the importance of the use of L-TRP in agriculture.