Map-based cloning of LPD, a major gene positively regulates leaf prickle development in eggplant.

KEY MESSAGE: A critical gene for leaf prickle development (LPD) in eggplant was mapped on chromosome E06 and was confirmed to be SmARF10B through RNA interference using a new genetic transformation technique called SACI developed in this study Prickles on eggplant pose challenges for agriculture and are undesirable in cultivated varieties. This study aimed to uncover the genetic mechanisms behind prickle formation in eggplant. Using the F2 and F2:3 populations derived from a cross between the prickly wild eggplant, YQ, and the prickle-free cultivated variety, YZQ, we identified a key genetic locus (LPD, leaf prickle development) on chromosome E06 associated with leaf prickle development through BSA-seq and QTL mapping. An auxin response factor gene, SmARF10B, was predicted as the candidate gene as it exhibited high expression in YQ's mature leaves, while being significantly low in YZQ. Downregulating SmARF10B in YQ through RNAi using a simple and efficient Agrobacterium-mediated genetic transformation method named Seedling Apical Cut Infection (SACI) developed in this study substantially reduced the size and density of leaf prickles, confirming the role of this gene in prickle development. Besides, an effective SNP was identified in SmARF10B, resulting in an amino acid change between YQ and YZQ. However, this SNP did not consistently correlate with prickle formation in eight other eggplant materials examined. This study sheds light on the pivotal role of SmARF10B in eggplant prickle development and introduces a new genetic transformation method for eggplant, paving the way for future research in this field.

Turgor regulation defect 1 proteins play a conserved role in pollen tube reproductive innovation of the angiosperms.

Sexual reproduction in angiosperms is siphonogamous, and the interaction between pollen tube and pistil is critical for successful fertilization. Our previous study demonstrated that mutation of the Arabidopsis turgor regulation defect 1 (TOD1) gene leads to reduced male fertility, a result of retarded pollen tube growth in the pistil. TOD1 encodes a Golgi-localized alkaline ceramidase, a key enzyme for the production of sphingosine-1-phosphate (S1P), which is involved in the regulation of turgor pressure in plant cells. However, whether TOD1s play a conserved role in the innovation of siphonogamy is largely unknown. In this study, we provide evidence that OsTOD1, which is similar to AtTOD1, is also preferentially expressed in rice pollen grains and pollen tubes. OsTOD1 knockout results in reduced pollen tube growth potential in rice pistil. Both the OsTOD1 genomic sequence with its own promoter and the coding sequence under the AtTOD1 promoter can partially rescue the attod1 mutant phenotype. Furthermore, TOD1s from other angiosperm species can partially rescue the attod1 mutant phenotype, while TOD1s from gymnosperm species are not able to complement the attod1 mutant phenotype. Our data suggest that TOD1 acts conservatively in angiosperms, and this opens up an opportunity to dissect the role of sphingolipids in pollen tube growth in angiosperms.

Construction of a High-Density Recombination Bin-Based Genetic Map Facilitates High-Resolution Mapping of a Major QTL Underlying Anthocyanin Pigmentation in Eggplant.

High-density genetic maps can significantly improve the resolution of QTL mapping. We constructed a high-density recombination bin-based genetic map of eggplant based on 200 F2 plants from an interspecific cross (Solanum melongena × S. incanum) using the whole genome resequencing strategy. The map was 2022.8 cM long, covering near 99% of the eggplant genome. The map contained 3776 bins, with 3644 (96.5%) being effective (position non-redundant) ones, giving a nominal average distance of 0.54 cM and an effective average distance of 0.56 cM between adjacent bins, respectively. Using this map and 172 F2:3 lines, a major QTL with pleiotropic effects on two anthocyanin pigmentation-related traits, leaf vein color (LVC) and fruit pericarp color (FPC), was steadily detected in a bin interval of 2.28 cM (or 1.68 Mb) on chromosome E10 in two cropping seasons, explaining ~65% and 55% of the phenotypic variation in LVC and FPC, respectively. Genome-wide association analysis in this population validated the QTL and demonstrated the correctness of mapping two bins of chromosome E02 onto E10. Bioinformatics analysis suggested that a WDR protein gene inside the bin interval with reliable effective variation between the two parents could be a possible candidate gene of the QTL.

Determination of absorption dose in chemical mutagenesis in plants.

Chemical mutagenesis is a useful tool for inducing mutations in plants. Seeds are often used as the material for chemical mutagenesis. The biological effect of a chemical mutagen on seeds is determined by absorption dose (the product of mutagen concentration and acting time, which starts after the mutagen is absorbed by the seeds). In practice, however, the concept of exposure dose (the product of mutagen concentration and treating time) is usually used instead because the time for absorbing mutagen is unknown. In this study, we conducted an experiment using ethyl methane sulphonate (EMS) to treat cauliflower seeds, in which five EMS concentrations (0%, 0.5%, 1.0%, 1.5% and 2.0%), three treating time lengths (4 h, 6 h and 8 h) and two pretreatments (non-presoaking and presoaking of seeds for 2 h) were set. We obtained a well-fitted nonlinear regression model for the relationship between seedling survival rate and the EMS treatment, and its marginal models for the two pretreatments. Based on the models, we determined the EMS absorption doses under the two different pretreatments and identified their 50% lethality dose (LD50). We found that presoaking could delay EMS absorption and therefore reduce the injury caused by EMS within a given treating time, but could hardly change the biological effect of EMS after it is absorbed. The conclusions about absorption dose and presoaking effect obtained in this study might be generally applicable to plant chemical mutagenesis in principle.