Qiang Wang

Carotenoids are present in most tissues of higher plants where they play a variety of essential roles. To study the regulation of carotenoid biosynthesis, we have isolated novel mutations in tomato (Solanum lycopersicum) with altered pigmentation of fruit or flowers. Here we describe the isolation and analysis of a tomato mutant, high-pigment 3 (hp3), that accumulates 30% more carotenoids in the mature fruit. Higher concentrations of carotenoids and chlorophyll were also measured in leaves and the pericarp of green fruit. The mutation in hp3 had occurred in the gene for zeaxanthin epoxidase (Zep), which converts zeaxanthin to violaxanthin. Consequently, leaves of the mutant lack violaxanthin and neoxanthin, and flowers contain only minute quantities of these xanthophylls. The concentration in the hp3 mutant of abscisic acid (ABA), which is derived from xanthophylls, is 75% lower than the normal level, making hp3 an ABA-deficient mutant. The plastid compartment size in fruit cells is at least twofold larger in hp3 plants compared with the wild-type. The transcript level in the green fruit of FtsZ, which encodes a tubulin-like protein involved in plastid division, is 60% higher in hp3 than in the wild-type, suggesting that increased plastid division is responsible for this phenomenon. Elevated fruit pigmentation and plastid compartment size were also observed in the ABA-deficient mutants flacca and sitiens. Taken together, these results suggest that ABA deficiency in the tomato mutant hp3 leads to enlargement of the plastid compartment size, probably by increasing plastid division, thus enabling greater biosynthesis and a higher storage capacity of the pigments.

Abstract Quickly and precisely gain genetically enhanced breeding elites with value-adding performance traits is desired by the crop breeders all the time. The present of gene editing technologies, especially the CRISPR/Cas9 system with the capacities of efficiency, versatility and multiplexing provides a reasonable expectation towards breeding goals. For exploiting possible application to accelerate the speed of process at breeding by CRISPR/Cas9 technology, in this study, the Agrobacterium tumefaciens -mediated CRISPR/Cas9 system transformation method was used for obtaining tomato ALC gene mutagenesis and replacement, in absence and presence of the homologous repair template. The average mutation frequency (72.73%) and low replacement efficiency (7.69%) were achieved in T 0 transgenic plants respectively. None of homozygous mutation was detected in T 0 transgenic plants, but one plant carry the heterozygous genes ( Cas9 / * - ALC / alc ) was stably transmitted to T 1 generations for segregation and genotyping. Finally, the desired alc homozygous mutants without T-DNA insertion (*/*- alc / alc ) in T 1 generations were acquired and further confirmed by genotype and phenotype characterization, with highlight of excellent storage performance, thus the recessive homozygous breeding elites with the character of long-shelf life were generated. Our results support that CRISPR/Cas9-induced gene replacement via HDR provides a valuable method for breeding elite innovation in tomato.

Microalgal lipid is one of the most promising feedstocks for biodiesel production. Chlorella appears to be a particularly good option, and nitrogen (N) starvation is an efficient environmental pressure used to increase lipid accumulation in Chlorella cells. The effects of N starvation of an oil-producing wild microalga, Chlorella sorokiniana C3, on lipid accumulation were investigated using thin layer chromatography (TLC), confocal laser scanning microscopy (CLSM) and flow cytometry (FCM). The results showed that N starvation resulted in lipid accumulation in C. sorokiniana C3 cells, oil droplet (OD) formation and significant lipid accumulation in cells were detected after 2 d and 8 d of N starvation, respectively. During OD formation, reduced photosynthetic rate, respiration rate and photochemistry efficiency accompanied by increased damage to PSII were observed, demonstrated by chlorophyll (Chl) fluorescence, 77K fluorescence and oxygen evolution tests. In the mean time the rate of cyclic electron transportation increased correspondingly to produce more ATP for triacylglycerols (TAGs) synthesis. And 0.5 d was found to be the turning point for the early stress response and acclimation of cells to N starvation. Increased level of membrane peroxidation was also observed during OD formation, and superoxide dismutase (SOD), peroxide dismutase (POD) and catalase (CAT) enzyme activity assays suggested impaired reactive oxygen species (ROS) scavenging ability. Significant neutral lipid accumulation was also observed by artificial oxidative stress induced by H2O2 treatment. These results suggested coupled neutral lipid accumulation and oxidative stress during N starvation in C. sorokiniana C3.

Microalgal lipids are highly promising feedstocks for biofuel production. Microalgal lipids, especially triacylglycerol, and practical applications of these compounds have received increasing attention in recent years. For the commercial use of microalgal lipids to be feasible, many fundamental biological questions must be addressed based on detailed studies of algal biology, including how lipid biosynthesis occurs and is regulated. Here, we review the current understanding of microalgal lipid biosynthesis, with a focus on the underlying regulatory mechanisms. We also present possible solutions for overcoming various obstacles to understanding the basic biology of microalgal lipid biosynthesis and the practical application of microalgae-based lipids. This review will provide a theoretical reference for both algal researchers and decision makers regarding the future directions of microalgal research, particularly pertaining to microalgal-based lipid biosynthesis.