As most soil phosphates exist as insoluble inorganic phosphate and organic phosphates, higher plants have developed several strategies for adaptation to low phosphorus (P). These include the secretion of acid phosphatase and organic acids, induction of the inorganic phosphate (Pi) transporter and the substitution of some enzyme activities as alternative pathways to increase P utilization efficiency. It has been proposed that plants also have a ' pho regulon' system, as observed in yeast and Escherichia coli ; however, the detail of the regulation system for gene expression on P status is still unclear in plants. To investigate the alteration of gene expression of rice roots grown under P-deficient conditions, a transcriptomic analysis was conducted using a cDNA microarray on rice. Based on the changes of gene expression under a -P treatment, the up-regulation of some genes due to P deficiency was confirmed. Some new important metabolic changes are suggested, namely: (1) acceleration of carbon supply for organic acid synthesis through glycolysis; (2) alteration of lipid metabolism; (3) rearrangement of compounds for cell wall; and (4) changes of gene expression related to the response for metallic elements such as Al, Fe and Zn.

Anthocyanins are secondary metabolites that contribute to colors of flowers, fruits and leaves. Asiatic hybrid lily (Lilium spp.) accumulates cyanidin anthocyanins in flower tepals, tepal spots and leaves of juvenile shoots. To clarify their mechanisms of regulation of anthocyanin pigmentation, two full-length cDNAs of R2R3-MYB (LhMYB6 and LhMYB12) were isolated from the anthocyanin-accumulating tepals of cultivar 'Montreux'. Analysis of the deduced amino acid sequences indicated they have homology with petunia AN2, homologous sequences of which had not been isolated in species of monocots. Yeast two-hybrid analysis showed that LhMYB6 and LhMYB12 interacted with the Lilium hybrid basic helix-loop-helix 2 (LhbHLH2) protein. Transient expression analysis indicated that co-expression of LhMYB6 and LhbHLH2 or LhMYB12 and LhbHLH2, introduced by a microprojectile, activated the transcription of anthocyanin biosynthesis genes in lily bulbscales. Spatial and temporal transcription of LhMYB6 and LhMYB12 was analyzed. The expression of LhMYB12 corresponded well with anthocyanin pigmentation in tepals, filaments and styles, and that of LhMYB6 correlated with anthocyanin spots in tepals and light-induced pigmentation in leaves. These results indicate that LhMYB6 and LhMYB12 positively regulate anthocyanin biosynthesis and determine organ- and tissue-specific accumulation of anthocyanin.

No abstract

Cluster root (CR) formation contributes much to the adaptation to phosphorus (P) deficiency. CR formation by white lupin (Lupinus albus L.) is affected by the P-limiting level in shoots, but not in roots. Thus, shoot-derived signals have been expected to transmit the message of P-deficiency to stimulate CR formation. In this study, it is shown that sugars are required for a response to P starvation including CR formation and the expression of P starvation-induced genes. White lupin plants were grown in vitro on P-sufficient or P-deficient media supplemented with sucrose for 4 weeks. Sucrose supply stimulated CR formation in plants on both P-sufficient and P-deficient media, but no CR appeared on the P-sufficient medium without sucrose. Glucose and fructose also stimulated CR formation on the P-sufficient medium. On the medium with sucrose, a high concentration of inorganic phosphate in leaves did not suppress CR formation. Because sorbitol or organic acid in the media did not stimulate CR formation, the sucrose effect was not due to increased osmotic pressure or enriched energy source, that is, sucrose acted as a signal. Gene transcription induced by P starvation, LaPT1 and LaPEPC3, was magnified by the combination of P limitation and sucrose feeding, and that of LaSAP was stimulated by sucrose supply independently of P supply. These results suggest that at least two sugar-signalling mediating systems control P starvation responses in white lupin roots. One system regulates CR formation and LaSAP expression, which acts even when P is sufficient if roots receive sugar as a signal. The other system controls LaPT1 and LaPEPC3 expression, which acts when P is insufficient.

BackgroundColor patterns in angiosperm flowers are produced by spatially and temporally restricted deposition of pigments. Identifying the mechanisms responsible for restricted pigment deposition is a topic of broad interest. Some dicots species develop bicolor petals, which are often caused by the post-transcriptional gene silencing (PTGS) of chalcone synthase (CHS) genes. An Asiatic hybrid lily (Lilium spp.) cultivar Lollypop develops bicolor tepals with pigmented tips and white bases. Here, we analyzed the global transcription of pigmented and non-pigmented tepal parts from Lollypop, to determine the main transcriptomic differences.ResultsDe novo assembly of RNA-seq data yielded 49,239 contigs (39,426 unigenes), which included a variety of novel transcripts, such as those involved in flavonoid-glycosylation and sequestration and in regulation of anthocyanin biosynthesis. Additionally, 1258 of the unigenes exhibited significantly differential expression between the tepal parts (false discovery rates <0.05). The pigmented tepal parts accumulated more anthocyanins, and unigenes annotated as anthocyanin biosynthesis genes (e.g., CHS, dihydroflavonol 4-reductase, and anthocyanidin synthase) were expressed 7–30-fold higher than those in non-pigmented parts. These results indicate that the transcriptional regulation of biosynthesis genes is more likely involved in the development of bicolor lily tepals rather than the PTGS of CHS genes. In addition, the expression level of a unigene homologous to LhMYB12, which often regulates full-tepal anthocyanin pigmentation in lilies, was >2-fold higher in the pigmented parts. Thus, LhMYB12 should be involved in the transcriptional regulation of the biosynthesis genes in bicolor tepals. Other factors that potentially suppress or enhance the expression of anthocyanin biosynthesis genes, including a WD40 gene, were identified, and their involvement in bicolor development is discussed.ConclusionsOur results indicate that the bicolor trait of Lollypop tepals is caused by the transcriptional regulation of anthocyanin biosynthesis genes and that the transcription profile of LhMYB12 provides a clue for elucidating the mechanisms of the trait. The tepal transcriptome constructed in this study will accelerate investigations of the genetic controls of anthocyanin color patterns, including the bicolor patterns, of Lilium spp.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2995-5) contains supplementary material, which is available to authorized users.

To elucidate the regulatory mechanisms of carotenoid accumulation in tepals of Asiatic hybrid lily (Lilium spp.), the content and composition of carotenoids and transcriptional changes of carotenoid biosynthetic genes were compared between tepals of yellow, red, pink and white flowers. Yellow and red tepal cultivars accumulated high amounts of carotenoids, and cultivars with pink and white tepals accumulated small amounts of carotenoids. Most of the carotenoids in yellow petals were antheraxanthin, (9Z)-violaxanthin, cis-lutein and violaxanthin. Capsanthin was accumulated in red tepals. Transcription of phytoene synthase, phytoene desaturase, f-carotene desaturase, carotenoid isomerase and b-ring hydroxylase in tepals increased as tepals grew. Among yellow and red tepal cultivars, the amounts of carotenoids were well associated with the transcription levels of biosynthetic genes, indicating that transcription levels regulate carotenoid accumulation in these cultivars. However, in pink and white tepals, the transcription levels of biosynthetic genes were similar to those in red tepals, indicating that small amounts of carotenoids are not explained by down-regulation of biosynthetic genes. Another factor should reduce carotenoid amounts in these tepals.

SummaryMany angiosperm families develop spatially regulated anthocyanin spots on their flowers. The Asiatic hybrid lily (Lilium spp.) cv 'Latvia' develops splatter-type spots on its tepals. The splatters arise simply from the deposition of anthocyanin pigments in the tepal epidermis.To determine how splatter development was regulated, we analysed the transcription of anthocyanin biosynthesis genes, and isolated and characterized an R2R3-MYB gene specific to splatter pigmentation.All anthocyanin biosynthesis genes were expressed in splatter-containing regions of tepals, but not in other regions, indicating that splatter pigmentation is caused by the transcriptional regulation of biosynthesis genes. Previously characterized LhMYB12 regulators were not involved in splatter pigmentation, but, instead, a new allele of the LhMYB12 gene, LhMYB12-Lat, isolated in this study, contributed to splatter development. In 'Latvia' and other lily plants expressing splatters, LhMYB12-Lat was preferentially transcribed in the splatter-containing region of tepals. Progeny segregation analysis showed that LhMYB12-Lat genotype and splatter phenotype were co-segregated among the F 1 population, indicating that LhMYB12-Lat determines the presence or absence of splatters.LhMYB12-Lat contributes to splatter development, but not to full-tepal pigmentation and raised spot pigmentation. As a result of its unique sequences and different transcription profiles, this new allele of LhMYB12 should be a novel R2R3-MYB specifically associating with splatter spot development.

No abstract