Ultra‐high α‐linolenic acid accumulating developmental defective embryo was rescued by lysophosphatidic acid acyltransferase 2

For decades, genetic engineering approaches to produce unusual fatty acids (UFAs) in crops has reached a bottleneck, including reduced seed oil production and seed vigor. Currently, plant models in the field of research are primarily used to investigate defects in oil production and seedling development, while the role of UFAs in embryonic developmental defects remains unknown. In this study, we developed a transgenic Arabidopsis plant model, in which the embryo exhibits severely wrinkled appearance owing to α‐linolenic acid (ALA) accumulation. RNA‐sequencing analysis in the defective embryo suggested that brassinosteroid synthesis, FA synthesis and photosynthesis were inhibited, while FA degradation, endoplasmic reticulum stress and oxidative stress were activated. Lipidomics analysis showed that ultra‐accumulated ALA is released from phosphatidylcholine as a free FA in cells, inducing severe endoplasmic reticulum and oxidative stress. Furthermore, we identified that overexpression of lysophosphatidic acid acyltransferase 2 rescued the defective phenotype. In the rescue line, the pool capacity of the Kennedy pathway was increased, and the esterification of ALA indirectly to triacylglycerol was enhanced to avoid stress. This study provides a plant model that aids in understanding the molecular mechanism of embryonic developmental defects and generates strategies to produce higher levels of UFAs.     

Sl‐lncRNA15492 interacts with Sl‐miR482a and affects Solanum lycopersicum immunity against Phytophthora infestans

Long non‐coding RNAs (lncRNAs) are involved in the resistance of plants to infection by pathogens via interactions with microRNAs (miRNAs). Long non‐coding RNAs are cleaved by miRNAs to produce phased small interfering RNAs (phasiRNAs), which, as competing endogenous RNAs (ceRNAs), function as decoys for mature miRNAs, thus inhibiting their expression, and contain pre‐miRNA sequences to produce mature miRNAs. However, whether lncRNAs and miRNAs mediate other molecular mechanisms during plant resistance to pathogens is unknown. In this study, as a positive regulator, Sl‐lncRNA15492 from tomato (Solanum lycopersicum Zaofen No. 2) plants affected tomato resistance to Phytophthora infestans. Gain‐ and loss‐of‐function experiments and RNA ligase‐mediated 5′‐amplification of cDNA ends (RLM‐5′ RACE) also revealed that Sl‐miR482a was negatively involved in tomato resistance by targeting Sl‐NBS‐LRR genes and that silencing of Sl‐NBS‐LRR1 decreased tomato resistance. Sl‐lncRNA15492 inhibited the expression of mature Sl‐miR482a, whose precursor was located within the antisense sequence of Sl‐lncRNA15492. Further degradome analysis and additional RLM‐5′ RACE experiments verified that mature Sl‐miR482a could also cleave Sl‐lncRNA15492. These results provide a mechanism by which lncRNAs might inhibit precursor miRNA expression through antisense strands of lncRNAs, and demonstrate that Sl‐lncRNA15492 and Sl‐miR482a mutually inhibit the maintenance of Sl‐NBS‐LRR1 homeostasis during tomato resistance to P. infestans.     

Overexpression of the persimmon abscisic acid β‐glucosidase gene (DkBG1) alters fruit ripening in transgenic tomato

β‐Glucosidases (BG) are present in many plant tissues. Among these, abscisic acid (ABA) β‐glucosidases are thought to take part in the adjustment of cellular ABA levels, however the role of ABA‐BG in fruits is still unclear. In this study, through RNA‐seq analysis of persimmon fruit, 10 full‐length DkBG genes were isolated and were all found to be expressed. In particular, DkBG1 was highly expressed in persimmon fruits with a maximum expression 95 days after full bloom (DAFD). We verified that, in vitro, DkBG1 protein can hydrolyze ABA‐glucose ester (ABA‐GE) to release free ABA. Compared with wild‐type, tomato plants that overexpressed DkBG1 significantly upregulated the expression of ABA receptor PYL3/7 genes and showed typical symptoms of ABA hypersensitivity in fruits. DkBG1 overexpression (DkBG1‐OE) accelerated fruit ripening onset by 3–4 days by increasing ABA levels at the pre‐breaker stage and induced early ethylene release compared with wild‐type fruits. DkBG1‐OE altered the expression of ripening regulator NON‐RIPENING (NOR) and its target genes; this in turn altered fruit quality traits such as coloration. Our results demonstrated that DkBG1 plays an important role in fruit ripening and quality by adjusting ABA levels via hydrolysis of ABA‐GE.     

Arabidopsis RING E3 ubiquitin ligase JUL1 participates in ABA‐mediated microtubule depolymerization,stomatal closure,and tolerance response to drought stress

Ubiquitination is a critical post‐translational protein modification that has been implicated in diverse cellular processes, including abiotic stress responses, in plants. In the present study, we identified and characterized a T‐DNA insertion mutant in the At5g10650 locus. Compared to wild‐type Arabidopsis plants, at5g10650 progeny were hyposensitive to ABA at the germination stage. At5g10650 possessed a single C‐terminal C3HC4‐type Really Interesting New Gene (RING) motif, which was essential for ABA‐mediated germination and E3 ligase activity in vitro. At5g10650 was closely associated with microtubules and microtubule‐associated proteins in Arabidopsis and tobacco leaf cells. Localization of At5g10650 to the nucleus was frequently observed. Unexpectedly, At5g10650 was identified as JAV1‐ASSOCIATED UBIQUITIN LIGASE1 (JUL1), which was recently reported to participate in the jasmonate signaling pathway. The jul1 knockout plants exhibited impaired ABA‐promoted stomatal closure. In addition, stomatal closure could not be induced by hydrogen peroxide and calcium in jul1 plants. jul1 guard cells accumulated wild‐type levels of H₂O₂ after ABA treatment. These findings indicated that JUL1 acts downstream of H₂O₂ and calcium in the ABA‐mediated stomatal closure pathway. Typical radial arrays of microtubules were maintained in jul1 guard cells after exposure to ABA, H₂O₂, and calcium, which in turn resulted in ABA‐hyposensitive stomatal movements. Finally, jul1 plants were markedly more susceptible to drought stress than wild‐type plants. Overall, our results suggest that the Arabidopsis RING E3 ligase JUL1 plays a critical role in ABA‐mediated microtubule disorganization, stomatal closure, and tolerance to drought stress.     

Flexible chromosome painting based on multiplex PCR of oligonucleotides and its application for comparative chromosome analyses in Cucumis

Chromosome painting is a powerful technique for chromosome and genome studies. We developed a flexible chromosome painting technique based on multiplex PCR of a synthetic oligonucleotide (oligo) library in cucumber (Cucumis sativus L., 2n = 14). Each oligo in the library was associated with a universal as well as nested specific primers for amplification, which allow the generation of different probes from the same oligo library. We were also able to generate double‐stranded labelled oligos, which produced much stronger signals than single‐stranded labelled oligos, by amplification using fluorophore‐conjugated primer pairs. Oligos covering cucumber chromosome 1 (Chr1) and chromosome 4 (Chr4) consisting of eight segments were synthesized in one library. Different oligo probes generated from the library painted the corresponding chromosomes/segments unambiguously, especially on pachytene chromosomes. This technique was then applied to study the homoeologous relationships among cucumber, C. hystrix and C. melo chromosomes based on cross‐species chromosome painting using Chr4 probes. We demonstrated that the probe was feasible to detect interspecies chromosome homoeologous relationships and chromosomal rearrangement events. Based on its advantages and great convenience, we anticipate that this flexible oligo‐painting technique has great potential for the studies of the structure, organization, and evolution of chromosomes in any species with a sequenced genome.