Phototropin-mediated perception of light direction in leaves regulates blade flattening

One conserved feature among angiosperms is the development of flat thin leaves. This developmental pattern optimizes light capture and gas exchange. The blue light (BL) receptors phototropins are required for leaf flattening, with the null phot1phot2 mutant showing curled leaves in Arabidopsis (Arabidopsis thaliana). However, key aspects of their function in leaf development remain unknown. Here, we performed a detailed spatiotemporal characterization of phototropin function in Arabidopsis leaves. We found that phototropins perceive light direction in the blade, and, similar to their role in hypocotyls, they control the spatial pattern of auxin signaling, possibly modulating auxin transport, to ultimately regulate cell expansion. Phototropin signaling components in the leaf partially differ from hypocotyls. Moreover, the light response on the upper and lower sides of the leaf blade suggests a partially distinct requirement of phototropin signaling components on each side. In particular, NON PHOTOTROPIC HYPOCOTYL 3 showed an adaxial-specific function. In addition, we show a prominent role of PHYTOCHROME KINASE SUBSTRATE 3 in leaf flattening. Among auxin transporters, PIN-FORMED 3,4,7 and AUXIN RESISTANT 1 (AUX1)/LIKE AUXIN RESISTANT 1 (LAX1) are required for the response while ABCB19 has a regulatory role. Overall, our results show that directional BL perception by phototropins is a key aspect of leaf development, integrating endogenous and exogenous signals.

LsaYAB7, A Homologous Gene of FILAMENTOUS FLOWER, Participating In The Regulation of Adaxial-Abaxial Polarity of Leaves In Lettuce

Background: The plant-specific YABBY transcription factor plays important roles in the development of lateral organs, the establishment of adaxial-abaxial polarity and abiotic stress response. However, the function of YABBY gene family in lettuce (Lactuca sativa), an important leaf vegetable is still unclear yet. Results: In this study, we analyzed the chromosomal distribution, gene structure and cis-transcriptional elements of the YABBY gene family in lettuce. Phylogenetic analysis of YABBY genes in lettuce, Arabidopsis, maize and rice classified them into five groups. In addition, the expression profile of YABBY genes in lettuce indicated that they may play distinct functions in different tissues and developmental processes. The subcellular localization analysis and transactivation assay showed that LsaYAB7 probably functions as a transcription factor in the nucleus. Furthermore, the ectopic expression of LsaYAB7 exhibited abaxially curled leaves, not only in Arabidopsis, but also in lettuce. Conclusion: Altogether, LsaYAB7 is a key functional gene in determining the adaxial-abaxial polarity of lettuce leaves. Our study laid foundation for the molecular research of functional genes in lettuce.

Fine mapping of the BnUC2 locus related to leaf up-curling and plant semi-dwarfing in Brassica napus

Background Studies of leaf shape development and plant stature have made important contributions to the fields of plant breeding and developmental biology. The optimization of leaf morphology and plant height to improve lodging resistance and photosynthetic efficiency, increase planting density and yield, and facilitate mechanized harvesting is a desirable goal in Brassica napus.Results Here, we investigated a B. napus germplasm resource exhibiting up-curled leaves and a semi-dwarf stature. In progeny populations derived from NJAU5737 and Zhongshuang 11 (ZS11), we found that the up-curled leaf trait was controlled by a dominant locus, BnUC2. We then fine mapped the BnUC2 locus onto an 83.19-kb interval on chromosome A05 using single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) markers. We further determined that BnUC2 was a major plant height QTL that explained approximately 70% of the phenotypic variation in two BC5F3 family populations derived from NJAU5737 and ZS11. This result implies that BnUC2 was also responsible for the observed semi-dwarf stature. The fine mapping interval of BnUC2 contained five genes, two of which, BnaA05g16700D (BnaA05.IAA2) and BnaA05g16720D, were revealed by comparative sequencing to be mutated in NJAU5737. This result suggests that the candidate gene mutation (BnaA05g16700D) in the conserved Degron motif GWPPV (P63S) was responsible for the BnUC2 locus. In addition, investigation of agronomic traits in a separation population indicated that plant height, main inflorescence length, and branching height were significantly reduced by BnUC2, whereas yield was not significantly altered. Our findings may provide an effective foundation for plant type breeding in B. napus.Conclusions Using SNP and SSR markers, a dominant locus (BnUC2) related to up-curled leaves and semi-dwarf stature in B. napus has been fine mapped onto an 83.19-kb interval of chromosome A05 containing five genes. The BnaA05g16700D (BnaA05.IAA2) is inferred to be candidate gene responsible for the BnUC2 locus.

TCO, a Putative Transcriptional Regulator in Arabidopsis, Is a Target of the Protein Kinase CK2

As multicellular organisms grow, spatial and temporal patterns of gene expression are strictly regulated to ensure that developmental programs are invoked at appropriate stages. In this work, we describe a putative transcriptional regulator in Arabidopsis, TACO LEAF (TCO), whose overexpression results in the ectopic activation of reproductive genes during vegetative growth. Isolated as an activation-tagged allele, tco-1D displays gene misexpression and phenotypic abnormalities, such as curled leaves and early flowering, characteristic of chromatin regulatory mutants. A role for TCO in this mode of transcriptional regulation is further supported by the subnuclear accumulation patterns of TCO protein and genetic interactions between tco-1D and chromatin modifier mutants. The endogenous expression pattern of TCO and gene misregulation in tco loss-of-function mutants indicate that this factor is involved in seed development. We also demonstrate that specific serine residues of TCO protein are targeted by the ubiquitous kinase CK2. Collectively, these results identify TCO as a novel regulator of gene expression whose activity is likely influenced by phosphorylation, as is the case with many chromatin regulators.

Rhizobium-induced elevation in xylem cytokinin delivery in pigeonpea induces changes in shoot development and leaf physiology

Inoculation with Rhizobium strain IC3342 induces in pigeonpea (Cajanus cajan (L) Millsp.) a leaf curl syndrome and elevated cytokinin levels in the xylem sap. High nitrogen (N) nutrition was found to inhibit onset of the syndrome which could then be induced by N-free nutrient after development of seven trifoliate leaves. This provided a new system to study the role of xylem cytokinin in shoot development and yielded plants suitable for determining the rate of delivery of xylem cytokinin to the shoot which for IC3342-inoculated plants was found to be three times that of control plants. Relative to leaves of control plants, the non-curled leaves of these IC3342 plants exhibited higher nitrogen and chlorophyll content and greater photosynthetic rate and stomatal conductance. Induction of the syndrome increased leaf thickness in developing leaves but not in expanded leaves already formed. Diameter of stems and number of laterals were also increased markedly by IC3342 inoculation which in addition induced leaf hyponasty. Exogenous cytokinins when applied directly to control leaves induced leaf curl and increased leaf thickness. The present studies are discussed in relation to the role of xylem cytokinins in plant development and especially the release of lateral buds from apical dominance.

First Report of Phytoplasmas Associated with the Degeneration Syndrome of Artichoke in Catalonia (Spain)

Spain is the second largest producer of artichoke (Cynara scolymus L.) in the world with 230,000 tons produced annually. The region of Catalonia, located in northeast Spain, has 3,500 ha dedicated to this crop. Low yield and degeneration anomalies are widespread problems in the Mediterranean area. The degeneration syndrome results in curled leaves and late development of capitulum. The association of this syndrome with different viruses such as Artichoke degeneration virus (ADV), Artichoke latent virus (ALV), Broad bean wilt virus (BBWV), Cucumber mosaic virus (CMV), and many others was not conclusive. Other studies indicated that this phenomenon could be related to a regression of the cultivar toward the species of origin, the wild cardoon (C. cardunculus L. var. sylvestris). The distribution of degenerated plants in the principal artichoke-growing areas of Catalonia together with the presence of plants with normal and degenerated tissues in the same plant suggested the presence of phytoplasmas. Samples from 30 symptomatic and 30 asymptomatic plants of cv. Blanca de Tudela were collected in February of 2006 from different areas of Catalonia and analyzed by PCR amplification of phytoplasma DNA. DNA for PCR analyses was prepared from leaf petioles and midribs according to the Ahrens and Seemüller procedure (1). Nested-PCR was carried out with rRNA primer pairs P1/P7 and fU5/rU3 (2,3). Alternatively, nested-PCR, with primers Tuf 1 f/r in the first step and Tuf AY f/r in the second, amplifying a DNA fragment of the elongation gene Tu of the phytoplasmas belonging to Aster yellows and stolbur groups was conducted (4). Results showed a high correlation between presence of symptoms and phytoplasma detection. Phytoplasmas were detected in 100% of the symptomatic plants (30 of 30) and only in one of the asymptomatic plants. The restriction fragment length profiles of Tuf AY amplicons with HpaII showed two different patterns, the most important belonging to the aster yellows (16SrI) group phytoplasma and the other to the stolbur (16SrXII) group phytoplasma. To our knowledge, this is the first time that phytoplasmas have been detected in artichoke and associated with degeneration of this crop. References: (1) U. Ahrens and E. Seemüller. Phytopathology 82:828, 1992. (2) S. Deng and C. Hiruki. J. Microbiol. Methods 14:53, 1991. (3) K. H. Lorenz et al. Phytopathology 85:771, 1995. (4) B. Schneider et al. Microbiology 143:3381, 1997.

Seasonal Dynamics of Taphrina deformans Inoculum in Peach Orchards

The dynamics of the inoculum of Taphrina deformans were studied during a 4-year period by (i) inspecting curled leaves for the presence of asci, (ii) placing deposition spore samplers within the tree canopies, and (iii) exposing potted peach plants (trap plants). These three approaches produced consistent results. Four main periods characterized the dynamics of the inoculum: the first period coincides with the parasitic stage of the pathogen's life cycle and the other periods with the saprophytic stage. Mid- to late spring (first period) was characterized by the presence of asci on infected leaves which produced and ejected large quantities of ascospores in 96% of the samplings. Rainfall was not necessary for ascospore dispersal, which was favored by air temperature <20°C and relative humidity ≥80% or wetness duration >8 h. In summer and autumn (second period), blastospores were trapped in 54 and 24% of samplings, respectively, with low spore numbers. In the winter (third period), blasto-spores were trapped in the lowest numbers and in only 6% of samplings. In late winter to early spring (fourth period), blastospores were found in 56% of samples, with increasing numbers. Rainfall significantly influenced blastospore dispersal and temperature was correlated with the seasonality found during the saprophytic stage.

The Potential for Green Fluorescent Protein as a Screening Tool in the Production of Haploid Potato

A hybrid between a highly regenerative diploid clone (BARD 1-3) of Solanum phureja and haploid inducer IVP 101 was transformed with Agrobacterium tumefaciens strain 4404 containing plasmid pHB2892 with genes for green florescent protein (GFP) and kanamycin resistance. Hemizygous primary transformants (To) were produced from three leaf discs: 17 diploid plants from one leaf disc, three and nine tetraploids from the other two leaf discs. GFP expression was observed qualitatively under fluorescence microscopes and quantitatively with a GFP meter. Segregation ratios for tetraploid T1 seedlings fit models for single duplex insertions (35 transgenic: 1 non) or double simplex insertions (15 transgenic: 1 non). Diploid T1 seedlings segregated for deleterious traits: dwarfed size and curled leaves, as well as the GFP transgene. Similar segregation patterns in diploid families implied that all diploids may have been from the same transformation event. The cumulative segregation showed the dwarfed and curled plants fit a single recessive gene ratio (3 normal: 1 mutant), and GFP fit a double-copy insertion ratio (15 transgenic: 1 non). Six T1 selections were free of deleterious traits, consistently high expressers of GFP, and produced fertile pollen.