Constitutive or seed‐specific overexpression of Arabidopsis G‐protein γ subunit 3 (AGG3) results in increased seed and oil production and improved stress tolerance in Camelina sativa

Heterotrimeric G‐proteins consisting of Gα, Gβ and Gγ subunits play an integral role in mediating multiple signalling pathways in plants. A novel, recently identified plant‐specific Gγ protein, AGG3, has been proposed to be an important regulator of organ size and mediator of stress responses in Arabidopsis, whereas its potential homologs in rice are major quantitative trait loci for seed size and panicle branching. To evaluate the role of AGG3 towards seed and oil yield improvement, the gene was overexpressed in Camelina sativa, an oilseed crop of the Brassicaceae family. Analysis of multiple homozygous T4 transgenic Camelina lines showed that constitutive overexpression of AGG3 resulted in faster vegetative as well as reproductive growth accompanied by an increase in photosynthetic efficiency. Moreover, when expressed constitutively or specifically in seed tissue, AGG3 was found to increase seed size, seed mass and seed number per plant by 15%–40%, effectively resulting in significantly higher oil yield per plant. AGG3 overexpressing Camelina plants also exhibited improved stress tolerance. These observations draw a strong link between the roles of AGG3 in regulating two critical yield parameters, seed traits and plant stress responses, and reveal an effective biotechnological tool to dramatically increase yield in agricultural crops.     

Redesign of the castorbean plant body plan for optimal combine harvesting

The seed oil of castorbean (Ricinus communis, Euphorbiaceae) is highly appreciated in several sectors of the chemical industry. A tropical perennial, with sympodial branching, this plant presents, at the same time, both vegetative shoots and inflorescences, as well as racemes with ripe seeds. This architecture is an obstacle to harvesting the plants using the standard combine harvester which requires, as with any other seed crop, that the plants be dry. One agronomic solution is to spray the plants with desiccants. However, in this paper a genetic solution is suggested, that is, an annual plant. This model is discussed within the present knowledge of plant monocarpic senescence. A mutation that changes the quantity and/or the quality of cambial activity could reduce the secondary growth in castorbean, thus favouring the plants death. Moreover, to stop iterative growth which is at the base of the perennial form of castorbean, a non‐branching model is also proposed. The occurrence of this phenotype in some crops (maize and sunflower) and mutants (tomato, barley, etc.) is examined. Considering apical dominance as the primary mechanism at the base of a non‐branching form, a mutation capable of inducing permanent dormancy of axillary buds is discussed. Both mutation breeding and genetic engineering are suggested as major tools to obtain an annual plant of castorbean.     

植物TCP转录因子的作用机理及其应用研究进展

TCP转录因子是一类植物特有蛋白,含有保守的TCP domain,其中由60个氨基酸组成的b HLH结构是结合DNA和蛋白互作所必需的。TCP转录因子由于其广泛参与调控植物的生长发育过程(如分枝、株高、叶型、花型等)而备受关注。最近有报道显示,TCP转录因子在植物逆境胁迫应答中(如低温和高盐)同样发挥重要作用。TCP蛋白参与多种信号转导途径(如油菜素内酯、茉莉酸、赤霉素、细胞分裂素等),可能是连接生长发育和介导胁迫响应的一个交叉点。本文从分子生物学角度,系统综述了植物TCP转录因子的作用机理及其在激素应答、发育调控及环境胁迫响应等过程中的功能,以期为基因工程方法改良作物生长模式和抗性提供参考。     

Ineffective utilization of nitrate by soybean during pod fill

The relative effectiveness of nitrate, allantoin, or nitrate plus allantoin as sources of nitrogen for the indeterminate soybean plant [ Glycine max (L.) Merr cv. Harper] was studied throughout vegetative and reproductive growth. All plants were provided with 3.0 m M nitrogen and were grown hydroponically in growth chambers. During vegetative and early reproductive growth, plants given nitrate or nitrate plus allantoin grew faster than plants provided allantoin only. However, during pod fill, plants provided with allantoin or allantoin plus nitrate gained weight more rapidly than plants receiving just nitrate. More importantly, at maturity plants that had been provided with allantoin or allantoin plus nitrate during pod fill were 30% heavier in total dry weight, 50% higher in nitrogen content, and 50% higher in seed yield than plants that had received just nitrate. At full bloom, all plants were inoculated with the same culture of Bradyrhizobium japonicum , and twice each week throughout pod fill each plant was assayed for nitrogen fixation (acetylene reduction). Correlation coefficients obtained by linear regression analysis show a strong positive correlation between the measured rate of nitrogen fixation and maximum plant fresh weight (r = 0.83), total plant nitrogen (r = 0.81), or seed yield (r = 0.76). The fact that nitrogen fixation during pod fill stimulates plant growth and seed yield, coupled with the facts that nitrate blocks nodulation and is not used efficiently during pod fill by the soybean plant, may explain why seed yield of field-grown soybeans usually does not respond to added fertilizer nitrogen. Thus, it is suggested that enhanced nitrogen fixation may be the key factor in improving soybean seed yield.     

Knockout of two BnaMAX1 homologs by CRISPR/Cas9‐targeted mutagenesis improves plant architecture and increases yield in rapeseed (Brassica napus L.)

Plant height and branch number are essential components of rapeseed plant architecture and are directly correlated with its yield. Presently, improvement of plant architecture is a major challenge in rapeseed breeding. In this study, we first verified that the two rapeseed BnaMAX1 genes had redundant functions resembling those of Arabidopsis MAX1, which regulates plant height and axillary bud outgrowth. Therefore, we designed two sgRNAs to edit these BnaMAX1 homologs using the CRISPR/Cas9 system. The T₀ plants were edited very efficiently (56.30%–67.38%) at the BnaMAX1 target sites resulting in homozygous, heterozygous, bi‐allelic and chimeric mutations. Transmission tests revealed that the mutations were passed on to the T₁ and T₂ progeny. We also obtained transgene‐free lines created by the CRISPR/Cas9 editing, and no mutations were detected in potential off‐target sites. Notably, simultaneous knockout of all four BnaMAX1 alleles resulted in semi‐dwarf and increased branching phenotypes with more siliques, contributing to increased yield per plant relative to wild type. Therefore, these semi‐dwarf and increased branching characteristics have the potential to help construct a rapeseed ideotype. Significantly, the editing resources obtained in our study provide desirable germplasm for further breeding of high yield in rapeseed.     

Field performance of maize grown from <Emphasis Type="Italic">Fusarium verticillioides</Emphasis>-inoculated seed

Fusarium verticillioides is an important fungus occupying dual roles in the maize plant. The fungus functions as an endophyte, a fungal/host interaction beneficial to the growth of some plants. At other times, the fungus may function as a mycotoxin producing pathogen. The advantages and/or disadvantages of the endophytic relationship must be established in order to target appropriate sites for controlling diseases and mycotoxins in maize. One possibility could be to ensure seed maize is fungal free prior to planting. Reciprocal inoculations were made with two fungal isolates on seed of two maize genotypes. Yield was measured at harvest by ear and seed characters and vegetative growth at one-month intervals for plant survival, height, weight and stem diameter. Yield and vegetative growth differed among mature plants only once based on seed inoculation status. In 1998, plant weight was reduced and seed weight per ear was increased for the dent maize, GT-MAS: gk, grown from F. verticillioides RRC 374- inoculated seed compared to other seed treatments. Most vegetative characters were reduced at the first collection for Silver Queen plants grown from F. verticillioides-inoculated seed in 1997 and 1999, but not in 1998. However, no significant differences occurred among mature Silver Queen plants during any of the three growing seasons. In conclusion, yield and vegetative growth of mature maize plants grown from F. verticillioides-inoculated seed were equal to or greater than plants grown from non-inoculated seed under south Georgia field conditions during 1997, 1998, and 1999.     

Effect of Asahi SL on China aster ‘Aleksandra’ seed yield, germination and some metabolic events

The effects of Asahi SL (sodium ortho and para-nitro phenolate, sodium 5 nitro guaiacolate) sprays on China aster plant height, seed yield and some metabolic events were investigated. The plants were sprayed with Asahi SL, in concentration of 0, 0.1, 0.2 or 0.4 %, three times before or during flowering, and six times before and during this stage. It was found that Asahi SL applied three times during flowering brought about an increase in the seed yield, germination and metabolic activity and did not modify vegetative growth of plants. The chemical used earlier, before flowering, had detrimental effect on seed yield and quality, although it stimulated vegetative growth. The positive effect of Asahi SL was more prominent in weather conditions unfavourable for seed production.