Shoot branching is among the most crucial morphological traits in rice (Oryza sativa L.) and is physiologically modulated by auxins, cytokinins (CKs), and strigolactones (SLs) cumulatively in rice. A number of studies focused on the interplay of these three hormones in regulating rice tiller extension. The present study primarily aimed at determining the impact of different treatments, which were used to regulate rice tiller and axillary bud development on node 2 at the tillering stage and full heading stage, respectively. Transcription levels of several genes were quantified through qRT-PCR analysis, and an endogenous auxin and four types of CKs were determined through LC-MS/MS. Both nutrient deficiency and exogenous SL supply were found to inhibit rice tiller outgrowth by reducing the CK content in the tiller buds. Furthermore, supplying the inhibitor of both exogenous SLs and endogenous SL synthesis could also affect the expression level of OsCKX genes but not the OsIPT genes. Comparison of OsCKX gene expression pattern under exogenous SL and CK supply suggested that the induction of OsCKX expression was most likely via a CK-induced independent pathway. These results combined with the expression of CK type-A RR genes in bud support a role for SLs in regulating bud outgrowth through the regulation of local CK levels. SL functioned antagonistically with CK in regulating the outgrowth of buds on node 2, by promoting the OsCKX gene expression in buds.

Iron (Fe) deficiency is a global health problem, especially in underdeveloped countries. Biofortification with genetic engineering methods has been used to improve Fe nutrition in a number of crops. Various steps, e.g., uptake, distribution, and storage, involved in Fe homeostasis have been manipulated to increase the Fe concentration in the edible portions of plants. Nicotianamine (NA) is an important metal ion chelator in plants. It promotes the mobility of Fe and decreases cellular Fe toxicity. Increasing the Fe content in crops by promoting NA synthesis could help decrease human diseases associated with Fe deficiency. In the present study, Arabidopsis thaliana nicotianamine synthase 1 (AtNAS1) was overexpressed in potato (Solanum tuberosum, St) under the control of the cauliflower mosaic virus 35S promoter. Transgenic plants had a significantly increased amount of Fe in tubers (52.7 µg/g dry weight, 2.4-fold the amount in wild-type tubers), while no differences in plant phenotype or yield were detected between transgenic and wild-type plants. The expression of genes involved in root mineral uptake and homeostasis, such as StYSL1, StIRT1, StFRO1, and StNAS, was also altered in the roots and leaves of the transgenic plants. Our results demonstrate that the manipulation of Fe chelation is a useful strategy for Fe nutrition improvement, and the increased Fe accumulation in tubers of transgenic potato plants is most likely caused by the increased movement of Fe from the leaf to the tuber.

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a catastrophic disease affecting kiwifruit worldwide. As no effective cure has been developed, planting Psa-resistant cultivars is the best way to avoid bacterial canker in kiwifruit cultivation. However, the differences in the mechanism of resistance between cultivars is poorly understood. In the present study, five local kiwifruit cultivars were used for Psa resistance evaluation and classified into different resistance categories, tolerant (T), susceptible (S), and highly susceptible (HS), based on their various symptoms of lesions on the cane. Susceptible and highly susceptible varieties had a higher sucrose concentration, and a greater decrease in sucrose content was observed after Psa inoculation in phloem than in tolerant varieties. Three invertase activities and their corresponding gene expressions were detected in the phloem with lesions and showed the same trends as the variations in sucrose concentration. Meanwhile, after Psa inoculation, enzyme activities involved in antioxidant defense responses, such as PAL, POD, and CAT, were also altered in the phloem of the lesion position. With no differences among cultivars, PAL and POD activities in phloem first increased and then decreased after Psa inoculation. However, great differences in CAT activities were observed between T and S/HS categories. Our results demonstrate that sucrose content was negatively correlated with the disease resistance of different cultivars and that the increase in immune response enzymes is likely caused by increased sucrose metabolism in the phloem.