Agustí Javier, Merelo Paz, Cercós Manuel, Tadeo Francisco R, Talón Manuel
Instituto Valenciano de Investigaciones Agrarias - Centro de Genómica, 46113 Moncada, Valencia, Spain.
BMC Plant Biol. 2009 Oct 23;9:127. doi: 10.1186/1471-2229-9-127.
Abscission is the cell separation process by which plants are able to shed organs. It has a great impact on the yield of most crop plants. At the same time, the process itself also constitutes an excellent model to study cell separation processes, since it occurs in concrete areas known as abscission zones (AZs) which are composed of a specific cell type. However, molecular approaches are generally hampered by the limited area and cell number constituting the AZ. Therefore, detailed studies at the resolution of cell type are of great relevance in order to accurately describe the process and to identify potential candidate genes for biotechnological applications.
Efficient protocols for the isolation of specific citrus cell types, namely laminar abscission zone (LAZ) and petiolar cortical (Pet) cells based on laser capture microdissection (LCM) and for RNA microextraction and amplification have been developed. A comparative transcriptome analysis between LAZ and Pet from citrus leaf explants subjected to an in-vitro 24 h ethylene treatment was performed utilising microarray hybridization and analysis. Our analyses of gene functional classes differentially represented in ethylene-treated LAZ revealed an activation program dominated by the expression of genes associated with protein synthesis, protein fate, cell type differentiation, development and transcription. The extensive repertoire of genes associated with cell wall biosynthesis and metabolism strongly suggests that LAZ layers activate both catabolic and anabolic wall modification pathways during the abscission program. In addition, over-representation of particular members of different transcription factor families suggests important roles for these genes in the differentiation of the effective cell separation layer within the many layers contained in the citrus LAZ. Preferential expression of stress-related and defensive genes in Pet reveals that this tissue is likely to be reprogrammed to prevent pathogen attacks and general abiotic stresses after organ shedding.
The LCM-based data generated in this survey represent the most accurate description of the main biological processes and genes involved in organ abscission in citrus. This study provides novel molecular insight into ethylene-promoted leaf abscission and identifies new putative target genes for characterization and manipulation of organ abscission in citrus.
脱落是植物器官脱落的细胞分离过程。它对大多数农作物的产量有很大影响。同时，该过程本身也构成了研究细胞分离过程的极佳模型，因为它发生在称为脱落区（AZs）的特定区域，该区域由特定类型的细胞组成。然而，分子方法通常受到构成AZ的面积有限和细胞数量较少的阻碍。因此，为了准确描述该过程并鉴定生物技术应用的潜在候选基因，在细胞类型分辨率上进行详细研究具有重要意义。
基于激光捕获显微切割（LCM）开发了用于分离特定柑橘细胞类型（即层状脱落区（LAZ）和叶柄皮层（Pet）细胞）以及RNA微量提取和扩增的有效方案。利用微阵列杂交和分析对经过体外24小时乙烯处理的柑橘叶片外植体的LAZ和Pet进行了比较转录组分析。我们对乙烯处理的LAZ中差异表达的基因功能类别分析表明，一个激活程序主要由与蛋白质合成、蛋白质命运、细胞类型分化、发育和转录相关的基因表达主导。与细胞壁生物合成和代谢相关的大量基因强烈表明，LAZ层在脱落程序中激活了分解代谢和合成代谢的细胞壁修饰途径。此外，不同转录因子家族的特定成员的过度表达表明这些基因在柑橘LAZ所含多层中的有效细胞分离层的分化中起重要作用。Pet中与应激相关和防御相关基因的优先表达表明，该组织可能会被重新编程以防止器官脱落后的病原体攻击和一般非生物胁迫。
本次调查中基于LCM生成的数据代表了对柑橘器官脱落中主要生物学过程和相关基因的最准确描述。本研究为乙烯促进的叶片脱落提供了新的分子见解，并鉴定了用于柑橘器官脱落表征和调控的新的假定靶基因。
