Hewitt Seanna, Kilian Benjamin, Koepke Tyson, Abarca Jonathan, Whiting Matthew, Dhingra Amit
Department of Horticulture, Washington State University, Pullman, WA 99163, USA.
Department of Agriculture, African Christian University, Lusaka H985+XQ3, Zambia.
Horticulturae. 2021 Sep;7(9). doi: 10.3390/horticulturae7090270. Epub 2021 Aug 30.
The harvesting of sweet cherry ( L.) fruit is a labor-intensive process. The mechanical harvesting of sweet cherry fruit is feasible; however, it is dependent on the formation of an abscission zone at the fruit-pedicel junction. The natural propensity for pedicel-fruit abscission zone (PFAZ) activation varies by cultivar, and the general molecular basis for PFAZ activation is not well characterized. In this study, ethylene-inducible change in pedicel fruit retention force (PFRF) was recorded in a developmental time-course with a concomitant analysis of the PFAZ transcriptome from three sweet cherry cultivars. In 'Skeena', mean PFRF for both control and treatment fruit dropped below the 0.40 kg-force (3.92 N) threshold for mechanical harvesting, indicating the activation of a discrete PFAZ. In 'Bing', mean PFRF for both control and treatment groups decreased over time. However, a mean PFRF conducive to mechanical harvesting was achieved only in the ethylene-treated fruit. While in 'Chelan' the mean PFRF of the control and treatment groups did not meet the threshold required for efficient mechanical harvesting. Transcriptome analysis of the PFAZ region followed by the functional annotation, differential expression analysis, and gene ontology (GO) enrichment analyses of the data facilitated the identification of phytohormone-responsive and abscission-related transcripts, as well as processes that exhibited differential expression and enrichment in a cultivar-dependent manner over the developmental time-course. Additionally, read alignment-based variant calling revealed several short variants in differentially expressed genes, associated with enriched gene ontologies and associated metabolic processes, lending potential insight into the genetic basis for different abscission responses between the cultivars. These results provide genetic targets for the induction or inhibition of PFAZ activation, depending on the desire to harvest the fruit with or without the stem attached. Understanding the genetic mechanisms underlying the development of the PFAZ will inform future cultivar development while laying a foundation for mechanized sweet cherry harvest.
甜樱桃（L.）果实的采收是一个劳动密集型过程。甜樱桃果实的机械采收是可行的；然而，这取决于在果实与果柄连接处形成离层区。果柄 - 果实离层区（PFAZ）激活的自然倾向因品种而异，并且PFAZ激活的一般分子基础尚未得到很好的表征。在本研究中，记录了在发育时间进程中乙烯诱导的果柄果实保持力（PFRF）变化，并同时分析了三个甜樱桃品种的PFAZ转录组。在‘斯基纳’品种中，对照和处理果实的平均PFRF均降至机械采收所需的0.40千克力（3.92牛）阈值以下，表明离散PFAZ被激活。在‘宾莹’品种中，对照和处理组的平均PFRF均随时间下降。然而，只有乙烯处理的果实达到了有利于机械采收的平均PFRF。而在‘奇兰’品种中，对照和处理组的平均PFRF均未达到高效机械采收所需的阈值。对PFAZ区域进行转录组分析，随后对数据进行功能注释、差异表达分析和基因本体（GO）富集分析，有助于鉴定植物激素响应和脱落相关转录本，以及在发育时间进程中以品种依赖方式表现出差异表达和富集的过程。此外，基于读段比对的变异检测揭示了差异表达基因中的几个短变异，这些变异与富集的基因本体和相关代谢过程相关，为了解品种间不同脱落反应的遗传基础提供了潜在线索。这些结果为根据带柄或不带柄采收果实的需求诱导或抑制PFAZ激活提供了遗传靶点。了解PFAZ发育的遗传机制将为未来品种培育提供信息，同时为甜樱桃机械化采收奠定基础。
