The distribution and content of auxin within plant tissues affect a variety of important growth and developmental processes. Polar auxin transport (PAT), mainly mediated by auxin influx and efflux transporters, plays a vital role in determining auxin maxima and gradients in plants. The auxin efflux carrier PIN-FORMED (PIN) family is one of the major protein families involved in PAT. Rice (Oryza sativa L.) genome possesses 12 OsPIN genes. However, the detailed functions of OsPIN genes involved in regulating the rice architecture and gravity response are less well understood. In the present study, OsPIN1b was disrupted by CRISPR/Cas9 technology, and its roles in modulating rice architecture and root gravitropism were investigated. Tissue-specific analysis showed that OsPIN1b was mainly expressed in roots, stems and sheaths at the seedling stage, and the transcript abundance was progressively decreased during the seedling stages. Expression of OsPIN1b could be quickly and greatly induced by NAA, indicating that OsPIN1b played a vital role in PAT. IAA homeostasis was disturbed in ospin1b mutants, as evidenced by the changed sensitivity of shoot and root to NAA and NPA treatment, respectively. Mutation of OsPIN1b resulted in pleiotropic phenotypes, including decreased growth of shoots and primary roots, reduced adventitious root number in rice seedlings, as well as shorter and narrower leaves, increased leaf angle, more tiller number and decreased plant height and panicle length at the late developmental stage. Moreover, ospin1b mutants displayed a curly root phenotype cultured with tap water regardless of lighting conditions, while nutrient solution culture could partially rescue the curly root phenotype in light and almost completely abolish this phenotype in darkness, indicating the involvement of the integration of light and nutrient signals in root gravitropism regulation. Additionally, amyloplast sedimentation was impaired in the peripheral tiers of the ospin1b root cap columella cell, while it was not the main contributor to the abnormal root gravitropism. These data suggest that OsPIN1b not only plays a vital role in regulating rice architecture but also functions in regulating root gravitropism by the integration of light and nutrient signals.
Phytohormone auxin plays a vital role in plant development and responses to environmental stresses. The spatial and temporal distribution of auxin mainly relies on the polar distribution of the PIN-FORMED (PIN) auxin efflux carriers. In this study, we dissected the functions of OsPIN9, a monocot-specific auxin efflux carrier gene, in modulating chilling tolerance in rice. The results showed that OsPIN9 expression was dramatically and rapidly suppressed by chilling stress (4°C) in rice seedlings. The homozygous ospin9 mutants were generated by CRISPR/Cas9 technology and employed for further research. ospin9 mutant roots and shoots were less sensitive to 1-naphthaleneacetic acid (NAA) and N-1-naphthylphthalamic acid (NPA), indicating the disturbance of auxin homeostasis in the ospin9 mutants. The chilling tolerance assay showed that ospin9 mutants were more tolerant to chilling stress than wild-type (WT) plants, as evidenced by increased survival rate, decreased membrane permeability, and reduced lipid peroxidation. However, the expression of well-known C-REPEAT BINDING FACTOR (CBF)/DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN 1 (DREB)-dependent transcriptional regulatory pathway and Ca2+ signaling genes was significantly induced only under normal conditions, implying that defense responses in ospin9 mutants have probably been triggered in advance under normal conditions. Histochemical staining of reactive oxygen species (ROS) by 3′3-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) showed that ospin9 mutants accumulated more ROS than WT at the early stage of chilling stress, while less ROS was observed at the later stage of chilling treatment in ospin9 mutants. Consistently, antioxidant enzyme activity, including catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), improved significantly during the early chilling treatments, while was kept similar to WT at the later stage of chilling treatment, implying that the enhanced chilling tolerance of ospin9 mutants is mainly attributed to the earlier induction of ROS and the improved ROS scavenging ability at the subsequent stages of chilling treatment. In summary, our results strongly suggest that the OsPIN9 gene regulates chilling tolerance by modulating ROS homeostasis in rice.
In recent years, there are many studies concentrating on the syntactic comprehensive ability of patients with Broca's aphasia who are all native English speakers. Among them, the mechanism of how patients comprehend passive sentences is concerned by many researchers. Contrastively, there are few studies on how native Chinese speakers with Broca's aphasia comprehend passive sentences. Based on relative theories and studies, such as Trace Deletion Hypothesis (TDH), Double Dependency Hypothesis (DDH) and the eye-tracking experiment aiming at English agrammatic patients, this paper focuses on one type of the Chinese passive sentence, sentence passive bei, raises a proposal that constructs a research scheme for Chinese agrammatic patients, puts forward a series of hypothetical results, and based on current solid theories, carries out various explanations for possible results.
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