Differential activation of sporamin expression in response to abiotic mechanical wounding and biotic herbivore attack in the sweet potato.
BACKGROUND
Plants respond differently to mechanical wounding and herbivore attack, using distinct pathways for defense. The versatile sweet potato sporamin possesses multiple biological functions in response to stress. However, the regulation of sporamin gene expression that is activated upon mechanical damage or herbivore attack has not been well studied.


RESULTS
Biochemical analysis revealed that different patterns of Reactive oxygen species (ROS) and antioxidant mechanism exist between mechanical wounding (MW) and herbivore attack (HA) in the sweet potato leaf. Using LC-ESI-MS (Liquid chromatography electrospray ionization mass spectrometry analysis), only the endogenous JA (jasmonic acid) level was found to increase dramatically after MW in a time-dependent manner, whereas both endogenous JA and SA (salicylic acid) increase in parallel after HA. Through yeast one-hybrid screening, two transcription factors IbNAC1 (no apical meristem (NAM), Arabidopsis transcription activation factor (ATAF), and cup-shaped cotyledon (CUC)) and IbWRKY1 were isolated, which interact with the sporamin promoter fragment of SWRE (sporamin wounding-responsive element) regulatory sequences. Exogenous application of MeJA (methyl jasmonate), SA and DIECA (diethyldithiocarbamic acid, JAs biosynthesis inhibitor) on sweet potato leaves was employed, and the results revealed that IbNAC1 mediated the expression of sporamin through a JA-dependent signaling pathway upon MW, whereas both IbNAC1 and IbWRKY1 coordinately regulated sporamin expression through JA- and SA-dependent pathways upon HA. Transcriptome analysis identified MYC2/4 and JAZ2/TIFY10A (jasmonate ZIM/tify-domain), the repressor and activator of JA and SA signaling among others, as the genes that play an intermediate role in the JA and SA pathways, and these results were further validated by qRT-PCR (quantitative real-time polymerase chain reaction).


CONCLUSIONS
This work has improved our understanding of the differential regulatory mechanism of sporamin expression. Our study illustrates that sweet potato sporamin expression is differentially induced upon abiotic MW and biotic HA that involves IbNAC1 and IbWRKY1 and is dependent on the JA and SA signaling pathways. Thus, we established a model to address the plant-wounding response upon physical and biotic damage.
SenthilKumar
S
Rajendran
I-Winnie
IW
Lin
Mei-Ju
MJ
Chen
Chien-Yu
CY
Chen
Institute of Plant Biology, National Taiwan University, Taipei 106, Taiwan. ykwbppp@ntu.edu.tw.
Kai-Wun
KW
Yeh
D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D001483:Base Sequence; D003517:Cyclopentanes / Q000378:metabolism / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D063990:Gene Ontology; D060434:Herbivory / Q000187:drug effects / Q000235:genetics*; D027723:Ipomoea batatas / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D008954:Models, Biological; D008969:Molecular Sequence Data; D054883:Oxylipins / Q000378:metabolism / Q000494:pharmacology; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D020156:Salicylic Acid / Q000378:metabolism / Q000494:pharmacology; D017422:Sequence Analysis, DNA; D026082:Singlet Oxygen / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D018411:Spodoptera / Q000187:drug effects / Q000502:physiology*; D013312:Stress, Physiological / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism; D059467:Transcriptome / Q000187:drug effects / Q000235:genetics; D020798:Two-Hybrid System Techniques
D000975:Antioxidants; D003517:Cyclopentanes; D004268:DNA-Binding Proteins; D054883:Oxylipins; D010940:Plant Proteins; D014157:Transcription Factors; C067142:sporamin protein, Ipomoea batatas; D026082:Singlet Oxygen; C011006:jasmonic acid; D020156:Salicylic Acid