Comparative Analysis of the Transcriptomes of Persisting and Abscised Fruitlets: Insights into Plant Hormone and Carbohydrate Metabolism Regulated Self-Thinning of Pecan Fruitlets during the Early Stage.

Jiyu Zhang,Tao Wang,Yongzhi Liu,Fan Zhang,Gang Wang

doi:10.3390/cimb44010013

Jiyu Zhang, Tao Wang + Show 3 more

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https://doi.org/10.3390/cimb44010013

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Abstract

Pecan is one of the most popular nut species in the world. The fruit drop rate of the pecan ‘Pawnee’ is more than 57%, with four fruit drop stages, which is very serious. In this study, we conducted transcriptomic profiling of persisting and abscised fruitlets in early fruit development by RNA-seq. A total of 11,976 differentially expressed genes (DEGs) were identified, 3012 upregulated and 8964 downregulated, in a comparison of abscised vs. persisting fruitlets at 35 days after anthesis (DAA). Our transcriptomic data suggest that gene subsets encoding elements involving the biosynthesis, metabolism, perception, signal transduction, and crosstalk of the plant hormones abscisic acid (ABA), auxin, cytokinin, ethylene, and gibberellin (GA) and plant growth regulators jasmonates, salicylic acid, and brassinosteroids were differentially expressed. In addition, the majority of transcriptionally activated genes involved in hormone signaling (except for ethylene and salicylic acid signaling) were downregulated in abscised fruitlets. The differential expression of transcripts coding for enzymes involved in sucrose, glucose, trehalose, starch, galactose, and galactinol metabolism shows that sucrose, galactinol, and glucose synthesis and starch content were reduced as starch biosynthesis was blocked, and retrogradation and degradation intensified. These results suggest that the abscised pecan fruitlets stopped growing and developing for some time before dropping, further indicating that their sugar supply was reduced or stopped. The transcriptome characterization described in this paper contributes to unravelling the molecular mechanisms and pathways involved in the physiological abscission of pecan fruits.

Highlights

Vegetative and reproductive organs that are senescent, infected, or damaged are shed from the main plant body, which is called abscission
Our analysis reveals that the transcriptional activity of genes involved in starch and sucrose metabolism and galactose metabolism were significantly regulated in the abscised fruitlets of pecan (Table 4 and Supplementary Table S4)
The fruit development and drop dynamics of the pecan ‘Pawnee’ were studied in this paper, and the results show that the fruit drop rate was more than 57%, suggesting that fruit drop was very serious

Summary

Introduction

Vegetative and reproductive organs that are senescent, infected, or damaged are shed from the main plant body, which is called abscission. Abscission is a specific sequence of highly complex regulated events [1]. The regulatory network activated by the abscising organ leads to the activation of abscission zones. The first step is the development of an abscission zone. The step is the activation of abscission signaling. Enzymatic hydrolysis takes place in the middle lamella of the abscission zone (AZ), and AZ cells begin to enlarge. The last step is the further differentiation 1and sealing of the abscission scar [2]

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