Nucleotide Variation in the NCED3 Region of Arabidopsis thaliana and its Association Study with Abscisic Acid Content under Drought Stress

Drought tolerance is a comprehensive quantitative trait that is being understood further at the molecular genetic level. Abscisic acid （ABA） is the main drought-induced hormone that regulates the expression of many genes related to drought responses. 9-cis-epoxycarotenoid dioxygenase （NCED3） is thought to be a key enzyme in ABA biosynthesis. In this paper, we measured the ABA content increase under drought stress, and sequenced and compared the sequence of AtNCED3 among 22 Arabidopsis thaliana accessions. The results showed that the fold of ABA content increase under drought stress was highly variable among these accessions. High density single nucleotide polymorphism （SNP） and insertion/deletion （indel） were found in the AtNCED3 region, on average one SNP per 87.4 bp and one indel per 502 bp. Nucleotide diversity was significantly lower in the coding region than that in non-coding regions. The results of an association study with ANOVA analysis suggested that the 274th site （P←→S） and the 327th site （P←→R） amino acid variations might be the cause of ABA content increase of 163av accession under drought stress.

Efficient and genotype independent maize transformation using pollen transfected by DNA-coated magnetic nanoparticles

Current gene delivery methods for maize are limited to specific genotypes and depend on timeconsuming and labor-intensive tissue culture techniques.Here,we report a new method to transfect maize that is culture-free and genotype independent.To enhance efficiency of DNA entry and maintain high pollen viability of 32%-55%,transfection was performed at cool temperature using pollen pretreated to open the germination aperture(40%–55%).Magnetic nanoparticles(MNPs)coated with DNA encoding either red fluorescent protein(RFP),β-glucuronidase gene(GUS),enhanced green fluorescent protein(EGFP)or bialaphos resistance(bar)was delivered into pollen grains,and female florets of maize inbred lines were pollinated.Red fluorescence was detected in 22%transfected pollen grains,and GUS stained 55%embryos at 18 d after pollination.Green fluorescence was detected in both silk filaments and immature kernels.The T1 generation of six inbred lines showed considerable EGFP or GUS transcripts(29%–74%)quantitated by polymerase chain reaction,and 5%–16%of the T1 seedlings showed immunologically active EGFP or GUS protein.Moreover,1.41%of the bar transfected T1 plants were glufosinate resistant,and heritable bar gene was integrated into the maize genome effectively as verified by DNA hybridization.These results demonstrate that exogenous DNA could be delivered efficiently into elite maize inbred lines recalcitrant to tissue culture-mediated transformation and expressed normally through our genotype-independent pollen transfection system.