These authors contributed equally to this work. SUMMARYPotassium transporters and channels play crucial roles in K + uptake and translocation in plant cells. These roles are essential for plant growth and development. AKT1 is an important K + channel in Arabidopsis roots that is involved in K + uptake. It is known that AKT1 is activated by a protein kinase CIPK23 interacting with two calcineurin B-like proteins CBL1/CBL9. The present study showed that another calcineurin B-like protein (CBL10) may also regulate AKT1 activity. The CBL10-over-expressing lines showed a phenotype as sensitive as that of the akt1 mutant under low-K + conditions. In addition, the K + content of both CBL10-over-expressing lines and akt1 mutant plants were significantly reduced compared with wild-type plants.Moreover, CBL10 directly interacted with AKT1, as verified in yeast two-hybrid, BiFC and co-immunoprecipitation experiments. The results of electrophysiological analysis in both Xenopus oocytes and Arabidopsis root cell protoplasts demonstrated that CBL10 impairs AKT1-mediated inward K + currents. Furthermore, the results from the yeast two-hybrid competition assay indicated that CBL10 may compete with CIPK23 for binding to AKT1 and negatively modulate AKT1 activity. The present study revealed a CBL-interacting protein kinase-independent regulatory mechanism of calcineurin B-like proteins in which CBL10 directly regulates AKT1 activity and affects ion homeostasis in plant cells.

Potassium (K + ) plays crucial roles in plant growth and development. In natural environments, K + availability in soils is relatively low and fluctuating. Transcriptional regulation of K + transporter genes is one of the most important mechanisms in the plant's response to K + deficiency. In this study, we demonstrated that the transcription factor ARF2 (Auxin Response Factor 2) modulates the expression of the K + transporter gene HAK5 (High Affinity K + transporter 5) in Arabidopsis thaliana. The arf2 mutant plants showed a tolerant phenotype similar to the HAK5-overexpressing lines on low-K + medium, whose primary root lengths were longer than those of wild-type plants. High-affinity K + uptake was significantly increased in these plants. ARF2-overexpressing lines and the hak5 mutant were both sensitive to low-K + stress. Disruption of HAK5 in the arf2 mutant abolished the low-K + -tolerant phenotype of arf2. As a transcriptional repressor, ARF2 directly bound to the HAK5 promoter and repressed HAK5 expression under K + sufficient conditions. ARF2 can be phosphorylated after low-K + treatment, which abolished its DNA binding activity to the HAK5 promoter and relieved the inhibition on HAK5 transcription. Therefore, HAK5 transcript could be induced, and HAK5-mediated high-affinity K + uptake was enhanced under K + deficient conditions. The presented results demonstrate that ARF2 plays important roles in the response to external K + supply in Arabidopsis and regulates HAK5 transcription accordingly.

Summary Indole‐3‐acetic acid (IAA) is a predominant form of active auxin in plants. In addition to de novo biosynthesis and release from its conjugate forms, IAA can be converted from its precursor indole‐3‐butyric acid (IBA). The IBA‐derived IAA may help drive root hair elongation in Arabidopsis thaliana seedlings, but how the IBA‐to‐IAA conversion is regulated and affects IAA function requires further investigation. In this study, HOMEOBOX PROTEIN 24 (HB24), a transcription factor in the zinc finger‐homeodomain family (ZF‐HD family) of proteins, was identified. With loss of HB24 function, defective growth occurred in root hairs. INDOLE‐3‐BUTYRIC ACID RESPONSE 1 (IBR1), which encodes an enzyme involved in the IBA‐to‐IAA conversion, was identified as a direct target of HB24 for the control of root hair elongation. The exogenous IAA or auxin analogue 1‐naphthalene acetic acid (NAA) both rescued the root hair growth phenotype of hb24 mutants, but IBA did not, suggesting a role for HB24 in the IBA‐to‐IAA conversion. Therefore, HB24 participates in root hair elongation by upregulating the expression of IBR1 and subsequently promoting the IBA‐to‐IAA conversion. Moreover, IAA also elevated the expression of HB24, suggesting a feedback loop is involved in IBA‐to‐IAA conversion‐mediated root hair elongation.

Rice seed proteins are lacking essential amino acids (EAAs). Genetic engineering offers a fast and sustainable method to solve this problem as it allows the specific expression of heterologous EAA-rich proteins. The use of selectable marker gene is essential for generation of transgenic crops, but might also lead to potential environmental and food safety problems. Therefore, the production of marker-free transgenic crops is becoming an extremely attractive alternative and could contribute to the public acceptance of transgenic crops. The present study was conducted to examine whether can be expressed specifically in rice seeds, and generate marker-free transgenic rice with improved nutritive value. was transferred into rice using-mediated co-transformation system with a twin T-DNA binary vector and its integration in rice genome was confirmed by southern blot. Transcription of was analyzed by Real-Time PCR and its expression was verified by western analysis. Protein and amino acid content were measured by the Kjeldahl method and the high-speed amino acid analyzer, respectively. Five selectable marker-free homozygous transgenic lines were obtained from the progeny. The expression of recombinant was confirmed by the observation of a 35 kDa band in SDS-PAGE and western blot. Compared to the wild-type control, the total protein contents in the seeds of five homozygous lines were increased by 1.06~12.87%. In addition, the content of several EAAs, including lysine, threonine, and valine was increased significantly in the best expressing line. The results indicated that the amino acid composition of rice grain could be improved by seed-specific expression of .

The formation of cell polarity is essential for many developmental processes such as polar cell growth and spatial patterning of cell division. A plant-specific ROP ( R h o -like GTPases from P lants) subfamily of conserved Rho GTPase plays a crucial role in the regulation of cell polarity. However, the functional study of ROPs in angiosperm is challenging because of their functional redundancy. The Marchantia polymorpha genome encodes a single ROP gene, Mp ROP , providing an excellent genetic system to study ROP-dependent signaling pathways. Mp rop knockout mutants exhibited rhizoid growth defects, and MpROP was localized at the tip of elongating rhizoids, establishing a role for MpROP in the control of polar cell growth and its functional conservation in plants. Furthermore, the Mp rop knockout mutant showed defects in the formation of meristem notches associated with disorganized cell division patterns. These results reveal a critical function of Mp ROP in the regulation of plant development. Interestingly, these phenotypes were complemented not only by Mp ROP but also Arabidopsis At ROP2 , supporting the conservation of ROP’s function among land plants. Our results demonstrate a great potential for M. polymorpha as a powerful genetic system for functional and mechanistic elucidation of ROP signaling pathways during plant development.