Expression of Flavone Synthase II and Flavonoid 3′-Hydroxylase is Associated with Color Variation in Tan-colored Injured Leaves of Sorghum

Sorghum (Sorghum bicolor L. Moench) exhibits various color changes in injured leaves in response to cutting stress. Here, we aimed to identify key genes for the light brown and dark brown color variations in tan-colored injured leaves of sorghum. For this purpose, sorghum M36001 (light brown injured leaves), Nakei-MS3B (purple), and a progeny, #7 (dark brown), from Nakei-MS3B × M36001, were used. Accumulated pigments were detected by using high-performance liquid chromatography: M36001 accumulated only apigenin in its light brown leaves; #7 accumulated both luteolin and a small amount of apigenin in its dark brown leaves, and Nakei-MS3B accumulated 3-deoxyanthocyanidins (apigeninidin and luteolinidin) in its purple leaves. Apigenin or luteolin glucoside derivatives were also accumulated, in different proportions. Differentially expressed genes before and after cutting stress were identified by using RNA-seq. Integration of our metabolic and RNA-seq analyses suggested that expression of only flavone synthase II (FNSII) led to the synthesis of apigenin in M36001, expression of both FNSII and flavonoid 3′-hydroxylase (F3′H) led to the synthesis of apigenin and luteolin in #7, and expression of both flavanone 4-reductase and F3’H led to the synthesis of 3-deoxyanthocyanidins in Nakei-MS3B. These results suggest that expression of FNSII is related to the synthesis of flavones (apigenin and luteolin) and the expression level of F3′H is related to the balance of apigenin and luteolin. Expression of FNSII and F3′H is thus associated with dark or light brown coloration in tan-colored injured leaves of sorghum

Overexpression of OsIRO2 improves both iron uptake and translocation to seeds in rice

Iron deficiency is a worldwide agricultural problem on calcareous soils with low iron (Fe) availability and also poses a major human nutritional problem. Plants induce Fe-acquisition systems under conditions of low Fe availability. Previously, we reported that an Fe deficiency-inducible bHLH transcription factor, OsIRO2, is responsible for regulating the genes involved in Fe homeostasis in rice. Here, we show that OsIRO2 overexpression results in improved tolerance to low Fe availability in calcareous soil. In addition to increased Fe content in shoots, rice overexpressing OsIRO2 accumulates more Fe in seeds than non-transformant rice when grown on calcareous soil. OsIRO2 promoter–GUS analysis revealed that OsIRO2 expression could be detected in developing seeds. These results suggest that OsIRO2 plays a crucial role in regulating both Fe uptake from soil and Fe translocation to grain. Improved uptake and translocation of Fe in the OsIRO2-overexpressing rice under low Fe availability provides an approach for producing graminaceous crops that are tolerant to Fe deficiency and have Fe-rich seeds to enhance production and the nutritional quality of food

Analysis of tomatoes showing iron deficiency symptoms in winter under heavy fruit load

Declines in crop productivity that are thought to be due to iron deficiency have been reported even on non-calcareous-alkaline soils. For example, tomatoes exhibit iron deficiency-like symptoms (yellowing of new leaves) if the fruit load is heavy during winter. The objective of this study is to investigate the relationship between fruit load, low temperatures, low sunlight, and iron deficiency, and to explore the possibility of increasing productivity with iron-containing fertilizers. Results of an investigation of the farms experiencing iron deficiency-like symptoms in winter showed low iron concentrations and elevated expression of iron deficiency-inducible genes in yellowing leaves. To investigate the effects of heavy fruit load on iron nutrition, plants were grown in three groups: those with a medium number of fruits per truss (MED), a high number of fruits (heavy fruit load; HEAVY), and a high number of fruits with additional iron fertilization (++Fe). The SPAD leaf-color value of the new leaves and weight of the lower leaves in winter were in the order of HEAVY < ++Fe < MED. In all groups, the iron concentrations in the upper leaves in January were lower than those in October and March. RNA-seq analysis showed that the expression of genes involved in iron absorption was suppressed in the roots in January, which may have contributed to iron deficiency in winter. These results suggest that one of the factors limiting the productivity of tomatoes in winter with heavy fruit load is iron, and that productivity can be restored by iron materials.</p

The novel transcription factor IDEF1 regulates iron-deficiency response and tolerance

Iron is essential for most living organisms and is required for normal plant growth. Plants induce iron utilization systems under conditions of low iron availability, but the molecular mechanisms of this gene regulation system remain largely unknown. We identified the rice transcription factor IDEF1, which specifically binds the iron-deficiency-responsive cis-acting element IDE1. IDEF1 belongs to an uncharacterized branch of the plant-specific transcription factor family ABI3/VP1 and efficiently binds to the CATGC sequence within IDE1. IDEF1 transcripts are constitutively present in rice roots and leaves. Transgenic tobacco plants expressing IDEF1 under the control of the constitutive cauliflower mosaic virus 35S promoter transactivate IDE1-mediated expression only in iron-deficient roots. Transgenic rice plants expressing IDEF1 under the control of the iron-deficiency-inducible IDS2 promoter tolerate iron deficiency in hydroponic culture and calcareous soil. Conversely, transgenic rice plants with repressed IDEF1 expression are susceptible to early stage iron deficiency in hydroponic culture. Expression analysis of these transgenic plants revealed that IDEF1 positively regulates iron-deficiency-induced genes, including the ferrous iron transporter gene OsIRT1 and the iron-deficiency-induced transcription factor gene OsIRO2. These data suggest the presence of a sequential gene regulatory network that functions via novel cis element/trans factor interactions to promote the iron-deficiency response

The novel transcription factor IDEF1 regulates iron-deficiency response and tolerance

Iron is essential for most living organisms and is required for normal plant growth. Plants induce iron utilization systems under conditions of low iron availability, but the molecular mechanisms of this gene regulation system remain largely unknown. We identified the rice transcription factor IDEF1, which specifically binds the iron-deficiency-responsive cis-acting element IDE1. IDEF1 belongs to an uncharacterized branch of the plant-specific transcription factor family ABI3/VP1 and efficiently binds to the CATGC sequence within IDE1. IDEF1 transcripts are constitutively present in rice roots and leaves. Transgenic tobacco plants expressing IDEF1 under the control of the constitutive cauliflower mosaic virus 35S promoter transactivate IDE1-mediated expression only in iron-deficient roots. Transgenic rice plants expressing IDEF1 under the control of the iron-deficiency-inducible IDS2 promoter tolerate iron deficiency in hydroponic culture and calcareous soil. Conversely, transgenic rice plants with repressed IDEF1 expression are susceptible to early stage iron deficiency in hydroponic culture. Expression analysis of these transgenic plants revealed that IDEF1 positively regulates iron-deficiency-induced genes, including the ferrous iron transporter gene OsIRT1 and the iron-deficiency-induced transcription factor gene OsIRO2. These data suggest the presence of a sequential gene regulatory network that functions via novel cis element/trans factor interactions to promote the iron-deficiency response

Analysis of the spatial expression patterns of rice iron deficiency-responsive element-binding factors IDEF1 and IDEF2

Iron (Fe) is critical for plant growth. Under conditions of low Fe availability, rice plants induce genes involved in Fe uptake and utilization. Recently, we identified the iron-deficiency-responsive cis-acting elements IDE1 and IDE2, which are bound in a specific manner by IDE-binding factors 1 and 2 (IDEF1 and IDEF2, respectively). IDEF1 and IDEF2 regulate genes related to the Fe-deficiency response. In the present study, we examined the spatial expression patterns of IDEF1 and IDEF2 during the germination, vegetative, and seed-maturation stages by assessing their localization in IDEF1 and IDEF2 promoter–GUS transgenic rice lines. During germination, IDEF1 and IDEF2 were expressed in the endosperm and embryo. In hydroponic culture experiments, the expression patterns of IDEF1 and IDEF2 were similar under both Fe-deficient and Fe-sufficient conditions during the vegetative stage. In leaves, IDEF1 expression was observed in mesophyll cells and in small vascular bundles, whereas IDEF2 was highly expressed in vascular bundles. In root sections, IDEF1 and IDEF2 were highly expressed in secondary roots and inside vascular bundles. IDEF1 was also expressed in pollen from flowers before and after anthesis, in the ovary after fertilization, and in the embryo during seed maturation. IDEF2 was expressed in flowering stage pollen, in immature seeds just after flowering, and in the dorsal vascular region during the late maturation stage. The spatial expression patterns of IDEF1 and IDEF2 partially overlapped with their target genes

A novel NAC transcription factor, IDEF2, which recognizes the iron deficiency-responsive element 2, regulates genes involved in iron homeostasis

Iron (Fe) is essential for most living organisms, and thus Fe deficiency poses a major abiotic stress in crop production. Plants induce Fe utilization systems under conditions of low-Fe availability, but the molecular mechanisms of gene regulation under Fe deficiency remain largely unknown. We identified a novel transcription factor in rice and barley, IDEF2, which specifically binds to the Fe deficiency-responsive cis-acting element 2 (IDE2), using yeast one-hybrid screening. IDEF2 belongs to an uncharacterized branch of the NAC transcription factor family and exhibits novel properties of sequence recognition. An electrophoretic mobility shift assay and cyclic amplification and selection of targets (CASTing) experiment revealed that IDEF2 predominantly recognizes CA[A/C]G[T/C][T/C/A][T/C/A] within IDE2 as the core binding site. IDEF2 transcripts are constitutively present in rice roots and leaves. Repression of the function of IDEF2 by RNA interference (RNAi) and chimeric repressor gene-silencing technology (CRES-T) caused aberrant Fe distribution between shoots and roots in rice grown hydroponically under Fe-sufficient or deficient conditions. These results reveal novel cis-element/trans-factor interactions that are functionally associated with iron homeostasis