AUTHOR=Guo Wei-Li , Chen Bi-Hua , Guo Yan-Yan , Yang He-Lian , Mu Jin-Yan , Wang Yan-Li , Li Xin-Zheng , Zhou Jun-Guo 

TITLE=Improved Powdery Mildew Resistance of Transgenic Nicotiana benthamiana Overexpressing the Cucurbita moschata CmSGT1 Gene

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00955

DOI=10.3389/fpls.2019.00955

ISSN=1664-462X

ABSTRACT=<p>Powdery mildew (PM), which is mainly caused by <italic>Podosphaera xanthii</italic>, is a serious biotrophic pathogen disease affecting field-grown and greenhouse-grown cucurbit crops worldwide. Because fungicides poorly control PM, the development and cultivation of PM-resistant varieties is critical. A homolog of <italic>SGT1</italic> (<italic>suppressor of the G2 allele of skp1</italic>), which encodes a key component of the plant disease-associated signal transduction pathway, was previously identified through a transcriptomic analysis of a PM-resistant pumpkin (<italic>Cucurbita moschata</italic>) inbred line infected with PM. In this study, we have characterized this <italic>SGT1</italic> homolog in <italic>C. moschata</italic>, and investigated its effects on biotic stress resistance. Subcellular localization results revealed that CmSGT1 is present in the nucleus. Additionally, <italic>CmSGT1</italic> expression levels in the PM-resistant material was strongly induced by PM, salicylic acid (SA) and hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>). In contrast, SA and H<sub>2</sub>O<sub>2</sub> downregulated <italic>CmSGT1</italic> expression in the PM-susceptible material. The ethephon (Eth) and methyl jasmonate (MeJA) treatments upregulated <italic>CmSGT1</italic> expression in both plant materials. The constitutive overexpression of <italic>CmSGT1</italic> in <italic>Nicotiana benthamiana</italic> (<italic>N. benthamiana</italic>) minimized the PM symptoms on the leaves of PM-infected seedlings, accelerated the onset of cell necrosis, and enhanced the accumulation of H<sub>2</sub>O<sub>2</sub>. Furthermore, the expression levels of <italic>PR1a</italic> and <italic>PR5</italic>, which are SA signaling transduction markers, were higher in the transgenic plants than in wild-type plants. Thus, the transgenic <italic>N. benthamiana</italic> plants were significantly more resistant to <italic>Erysiphe cichoracearum</italic> than the wild-type plants. This increased resistance was correlated with cell death, H<sub>2</sub>O<sub>2</sub> accumulation, and upregulated expression of SA-dependent defense genes. However, the chlorosis and yellowing of plant materials and the concentration of bacteria at infection sites were greater in the transgenic <italic>N. benthamiana</italic> plants than in the wild-type plants in response to infections by the pathogens responsible for bacterial wilt and scab. Therefore, <italic>CmSGT1</italic>-overexpressing <italic>N. benthamiana</italic> plants were hypersensitive to these two diseases. The results of this study may represent valuable genetic information for the breeding of disease-resistant pumpkin varieties, and may also help to reveal the molecular mechanism underlying CmSGT1 functions.</p>