What can hornworts teach us?

The hornworts are a small group of land plants, consisting of only 11 families and approximately 220 species. Despite their small size as a group, their phylogenetic position and unique biology are of great importance. Hornworts, together with mosses and liverworts, form the monophyletic group of bryophytes that is sister to all other land plants (Tracheophytes). It is only recently that hornworts became amenable to experimental investigation with the establishment of Anthoceros agrestis as a model system. In this perspective, we summarize the recent advances in the development of A. agrestis as an experimental system and compare it with other plant model systems. We also discuss how A. agrestis can help to further research in comparative developmental studies across land plants and to solve key questions of plant biology associated with the colonization of the terrestrial environment. Finally, we explore the significance of A. agrestis in crop improvement and synthetic biology applications in general.

An Agrobacterium-mediated stable transformation technique for the hornwort model Anthoceros agrestis.

Despite their key phylogenetic position and their unique biology, hornworts have been widely overlooked. Until recently there was no hornwort model species amenable to systematic experimental investigation. Anthoceros agrestis has been proposed as the model species to study hornwort biology. We have developed an Agrobacterium-mediated method for the stable transformation of A. agrestis, a hornwort model species for which a genetic manipulation technique was not yet available. High transformation efficiency was achieved by using thallus tissue grown under low light conditions. We generated a total of 274 transgenic A. agrestis lines expressing the ß-glucuronidase (GUS), cyan, green, and yellow fluorescent proteins under control of the CaMV 35S promoter and several endogenous promoters. Nuclear and plasma membrane localization with multiple color fluorescent proteins was also confirmed. The transformation technique described here should pave the way for detailed molecular and genetic studies of hornwort biology, providing much needed insight into the molecular mechanisms underlying symbiosis, carbon-concentrating mechanism, RNA editing and land plant evolution in general.

Spatial patterning of scent in petunia corolla is discriminated by bees and involves the ABCG1 transporter.

Floral guides are patterned cues that direct the pollinator to the plant reproductive organs. The spatial distribution of showy visual and olfactory traits allows efficient plant-pollinator interactions. Data on the mechanisms underlying floral volatile patterns or their interactions with pollinators are lacking. Here we characterize the spatial emission patterns of volatiles from the corolla of the model plant Petunia × hybrida and reveal the ability of honeybees to distinguish these patterns. Along the adaxial epidermis, in correlation with cell density, the petal base adjacent to reproductive organs emitted significantly higher levels of volatiles than the distal petal rim. Volatile emission could also be differentiated between the two epidermal surfaces: emission from the adaxial side was significantly higher than that from the abaxial side. Similar emission patterns were also observed in other petunias, Dianthus caryophyllus (carnation) and Argyranthemum frutescens (Marguerite daisy). Analyses of transcripts involved in volatile production/emission revealed lower levels of the plasma-membrane transporter ABCG1 in the abaxial versus adaxial epidermis. Transient overexpression of ABCG1 enhanced emission from the abaxial epidermis to the level of the adaxial epidermis, suggesting its involvement in spatial emission patterns in the epidermal layers. Proboscis extension response experiments showed that differences in emission levels along the adaxial epidermis, that is, petal base versus rim, detected by GC-MS are also discernible by honeybees.

Ectopic Expression of PAP1 Leads to Anthocyanin Accumulation and Novel Floral Color in Genetically Engineered Goldenrod (Solidago canadensis L.).

Floral pigmentation is of major importance to the ornamental industry, which is constantly searching for cultivars with novel colors. Goldenrod (Solidago canadensis) has monochromatic yellow carotenoid-containing flowers that cannot be modified using classical breeding approaches due to a limited gene pool. To generate Solidago with novel colors through metabolic engineering, we first developed a procedure for its regeneration and transformation. Applicability of different cytokinins for adventitious regeneration was examined in the commercial cv. Tara, with zeatin yielding higher efficiency than 6-benzylaminopurine or thidiazuron. A comparison of regeneration of commercial cvs. Tara, Golden Glory and Ivory Glory revealed Tara to be the most potent, with an efficiency of 86% (number of shoots per 100 leaf explants). Agrobacterium-based transformation efficiency was highest for cv. Golden Glory (5 independent transgenic shoots per 100 explants) based on kanamycin selection and the GUS reporter gene. In an attempt to promote anthocyanin biosynthesis, we generated transgenic Solidago expressing snapdragon (Antirrhinum majus) Rosea1 and Delila, as well as Arabidopsis thaliana PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1) transcription factors. Transgenic cv. Golden Glory expressing cauliflower mosaic virus 35S-driven PAP1 generated red flowers that accumulated delphinidin and its methylated derivatives, as compared to control yellow flowers in the GUS-expressing plants. The protocol described here allows efficient engineering of Solidago for novel coloration and improved agricultural traits.

[Effects of debagging time and picking off leaf on fruit quality of "Red Fuji" apple].

This paper studied the effects of debagging time and picking off leaves around fruits on the fruit quality and 1-year old shoots stored nutrition of "Red Fuji" apple. Properly advancing debagging time significantly increased the mean mass, anthocyanin content, and coloration area of the fruits (P < 0.05). Comparing with those of the fruits debagged on September 30, the mean mass, anthocyanin content, and coloration area of the fruits debagged on September 24 increased by 10.98%, 28.15%, and 13.44%, respectively, and the fruit firmness, soluble solid content, and titratable acidity had less differences. When the leaves within 15, 30, and 45 cm away from the fruits were wholly picked off, the light environment around the fruits improved significantly (P < 0.01), with the light intensity increased by 70%, 95%, and 115%, respectively, compared with no leaf picked off treatment. Picking off the leaves within 30-45 cm away from the fruits benefited the fruit coloration and anthocyanin accumulation. No significant effects were observed on the 1-year old shoots stored nutrition and their budding in next year among the treatments of picking off leaves. Advancing debagging time and picking off the leaves within 30-45 cm away from the fruits could improve fruit appearance and quality.

[Effects of different pruning modes on the light distribution characters and fruit yield and quality in densely planted 'Red Fuji' apple orchard].

This paper studied the effects of different pruning modes on the light distribution at different positions of canopy and the fruit yield and quality in different layers in a densely planted 'Red Fuji' apple orchard. Comparing with no pruning, both light and heavy pruning improved the light distribution in the canopy. Under light pruning, the canopy volume with a relative light intensity less than 30% occupied 14. 6% of the total, and that with a relative light intensity more than 80% accounted for 11.2%. Under heavy pruning, the two values were 12.8% and 28.8%, respectively. The fruit yield under light pruning increased in the first year, but that under heavy pruning decreased, with the fruit quality being both improved. The mean fruit mass, firmness, and soluble solid matter content decreased in the order of light pruning > heavy pruning > no pruning, the titratable acid content was in adverse, and the anthocyanin content was in the order of heavy pruning > light pruning > no pruning. From the viewpoint of fruit yield and quality, light pruning was the best modification mode for densely planted orchards.

[Effects of alternative partial rootzone irrigation on peach growth, productivity, and water use efficiency].

Taking 12-year-old peach (Prunus persica L. Batsch cv. Ruiguang 5) as test material, this paper studied the effects of alternative partial rootzone irrigation (APRI) on its growth, productivity, and water use efficiency under semi-arid climate condition. The results showed that in APRI treatments, the soil water content in the wet side of peach tree decreased with increasing soil depth, while that in the dry side was in adverse, with the maximal difference appeared in 0-25 cm soil layer. In the treatments of APRI with an interval of 2 and 4 weeks, the leaf water potential at pre-dawn was lower than that in the control (sufficient irrigation), but with the time prolonged, this potential in all treatments tended to decrease, and had no significant difference in the afternoon. The peach yield in APRI treatments was 10% lower than that in the control, but the irrigation amount was reduced by 50%, and the water use efficiency was increased by 75%. APRI significantly limited the shoot growth of peach tree, but had no obvious effect on the fruit diameter.