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Title: Transcriptome profiling of petal abscission zone and functional analysis of AUX/IAA family genes reveal that RhIAA16 is involved in petal shedding in rose

Author
item GAO, YUERONG - China Agricultural University
item LIU, CHUN - China Agricultural University
item LI, XIAODONG - China Agricultural University
item XU, HAIQIAN - China Agricultural University
item LIANG, YUE - China Agricultural University
item FEI, ZHANGJUN - US Department Of Agriculture (USDA)
item GAO, JUNPING - China Agricultural University
item Jiang, Cai-Zhong
item MA, CHAO - China Agricultural University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2016
Publication Date: 9/15/2016
Citation: Gao, Y., Liu, C., Li, X., Xu, H., Liang, Y., Fei, Z., Gao, J., Jiang, C., Ma, C. 2016. Transcriptome profiling of petal abscission zone and functional analysis of AUX/IAA family genes reveal that RhIAA16 is involved in petal shedding in rose. Frontiers in Plant Science. 7:1375. doi: 10.3389/fpls.2016.01375.

Interpretive Summary: Plant organ abscission is a crucial process that occurs throughout the life span of plants. The abscission regulates the detachment of organs from main body. This will benefit plants for recycling nutrients for continuous growth, propagating, facilitating reproduction, and preventing from disease infections. In particular, flower, fruit and seed abscission is closely correlated with plant reproductive success, crop quality, and productivity. Initiation of flower organ abscission is triggered by both internal and external cues. As internal cues, interaction of auxin and ethylene plays a critical role in abscission initiation. Depletion of the polar flow of auxin passing through the abscission zone (AZ) makes the AZ sensitive to ethylene, which triggers the separation process. On the contrary, auxin as a negative regulator of abscission inhibits the cell separation process. The change in auxin flow results in the changes of transcript abundance of many genes involved in auxin biosynthesis, signal transduction, and transport. Functional studies of Auxin Response Factors (ARFs) 1, 2, 7, and 19 demonstrated that these transcriptional regulators have functions in floral organ abscission. However, the roles of other gene families in the auxin pathway in the regulation of the petal abscission process are still largely unknown. The perception and transduction of auxin signaling involve the cooperative action of several components. Among them, auxin/indole-3-acetic acid (AUX/IAA) proteins act as transcription repressors by dimerizing with auxin response factors (ARFs). In presence of auxin, AUX/IAA binding to the transport inhibitor response1/auxin signaling F-box (TIR1/AFB) leads to the degradation of AUX/IAA protein, follows by releasing ARF to trigger the expression of auxin responsive genes. However, the role of AUX/IAAs in flower petal abscission is not well documented. Roses are one of the most important cut flowers among ornamental plants. The opening and longevity of rose flower are major factors in determining the ornamental value of rose flower. Moreover, the rose flower longevity is largely dependent on the timing of petal shedding occurrence. However, the information of molecular mechanism governing the rose petal abscission is scarce. To date, the regulatory genes in abscission signaling pathway, including IDA, NEVERSHED, EVERSHED, were identified and characterized in model plants by genetic mapping of mutants. This forward genetic technique is difficult and time-consuming to identify and characterize the genes in non-model plant systems including rose. Next generation sequencing technology has become an effective method to investigate the regulatory network of abscission. Transcriptome studies of flower abscission process were previously performed in several plant species including tomato, olive, melon, apple, and litchi. Most of those studies focus on dissecting the regulatory mechanism of pedicel abscission that is the last phase of fruit development and the ripening process. Combined with reverse genetic techniques, roles of several genes obtained from those transcriptome data related to abscission have been confirmed, including SlERF52 and KD1. In Arabidopsis, HAESA (HAE) and HAESA-LIKE2 (HSL2)-dependent pathways were revealed to be involved in petal AZ by the comparison of the transcriptomes of wild-type and hae hsl2 double mutant. However, the mechanism regulating petal abscission in non-model plants is still not well understood. Here, we attempt to investigate the transcriptome dynamics of the petal abscission zone during petal shedding in rose by Pyro-sequencing technology and to dissect transcriptional networks governing abscission process. Furthermore, we identified and characterized an AUX/IAA gene, RhIAA16, which played an important role in the controlling of petal abscission in rose.

Technical Abstract: Rose is one of the most important cut flowers among ornamental plants. Rose flower longevity is largely dependent on the timing of petal shedding occurrence. To understand the molecular mechanism underlying petal abscission in rose, we performed transcriptome profiling of the petal abscission zone during petal shedding using the Pyro-sequencing technology. We identified a total of 2592 differentially transcribed genes (DTGs) during rose petal shedding. Gene ontology (GO) term enrichment and biochemical pathway analyses showed that abscission resulted in changes in single-organism process, single-organism cellular process, and response to broad stimulus. Among these DTGs, approximately 150 genes putatively encoding transcription factors (TFs) were identified in rose abscission zone. These included zinc finger, WRKY, ERF, and AUX/IAA gene families, suggesting a complex transcriptional reprogramming of petal abscission. In particular, approximately 108 DTGs were related to hormone pathways, of which auxin and ethylene related DTGs are the largest groups including 52 and 41 genes, respectively. Moreover, among DTGs related to auxin, we identified an AUX/IAA gene RhIAA16 that was up-regulated in response to petal shedding. Silencing RhIAA16 by virus-induced gene silencing in rose promoted petal abscission, suggesting that RhIAA16 plays an important role in rose petal abscission.