Early fruit abscission is associated with the IAA14/SLR-ARF7 signaling cascade in pedicels of self-abscising apple

The self-abscising characteristic of fruit is a prominent trait for labor-saving cultivation in apple (Malus × domestica). Up to 30 days after full bloom, early abscission leaves only central fruit in a cluster, while four lateral fruits are abscised. Since fruit abscission is possibly induced during earlier phases of fruit development, samples were collected at full bloom and 10 days after full bloom. Comparative analysis between central and lateral pedicels in self-abscising apple can be used to identify the genes that trigger the abscission mechanism, as the destinies of the pedicels in a cluster are obvious. Transcriptome analysis was performed using RNA-Seq to compare expression profiles between the surviving central pedicel to be survived and abscised lateral pedicel to be abscised from self-abscising apple. A total of 797,647 ESTs were assembled into 65,876 contigs which were annotated and analyzed with using Blast2GO. A total of 1,585 differentially expressed genes in central and lateral pedicels were identified using the NOISeq software. , and these genes were were characterized using the MapMan ontology software. Transcription factors involved in vascular bundle differentiation functioned in the central pedicel, while the signaling cascade of IAA14/SLR-ARF7, which progressed during lateral root emergence from primary roots, operated in lateral pedicels. Future studies should explore associations between the mechanisms of lateral root emergence and pedicel abscission during early phases of fruit development, as well as the interconnection among hormones. Overall design: mRNA profile of 2 different pedicel tissue of apple using 454 GS-FLX

苹果（Malus × domestica）的果实自脱落特性是其省力化栽培的关键性状。在盛花期后至多30天内，早期脱落仅保留果簇中的中心果实，4枚侧生果实随之脱落。由于果实脱落可能在果实发育的更早阶段即被启动，研究团队于盛花期及盛花期后10天采集了实验样本。通过对比具有自脱落特性苹果的中心果柄与侧生果柄的表达谱，可鉴定触发脱落机制的相关基因，因为同一果簇内不同果柄的发育命运差异显著。

本研究通过RNA测序（RNA-Seq）开展转录组分析，对比待保留的中心果柄与即将脱落的侧生果柄的基因表达谱。总计797,647条表达序列标签（Expressed Sequence Tags, ESTs）被组装为65,876个重叠群（contigs），并通过Blast2GO软件完成注释与功能分析。借助NOISeq软件，研究共鉴定出1,585个在中心果柄与侧生果柄间差异表达的基因，随后使用MapMan本体论软件对这些差异基因进行了功能表征。

分析结果显示，在中心果柄中，参与维管束分化的转录因子发挥调控功能；而在侧生果柄中，则激活了初生根侧根发生过程中运作的IAA14/SLR-ARF7信号级联反应。

未来研究可进一步探索果实发育早期阶段侧根发生机制与果柄脱落之间的关联，以及各类激素间的相互调控网络。

实验整体设计：以具有自脱落特性的苹果的2种不同果柄组织为材料，采用454 GS-FLX测序平台进行mRNA表达谱分析。