Introduction
In their natural inhabits, plants are inevitably exposed to different biotic and abiotic stresses individually or simultaneously and have to appropriately respond to the diverse stresses to maximize fitness. As the resource is limited, and the stress response is costly, the defense response to the stress with the greatest threat is usually prioritized by repressing growth and unnecessary defense response to the stresses that are absent or not so serious(Lozano-Duran et al., 2013), thus result in extensive tradeoff among plant growth and response to different stresses (Berens et al., 2019; Huot, Yao, Montgomery, & He, 2014). HTS and pathogen attack are two closely related stresses frequently encountered by plants in tropical or subtropical climates, plant immune responses to pathogens are generally dampened(Hua, 2013) but in some case promoted(Onaga et al., 2017) by HTS. ABA, a crucial regulator in plant thermotolerance(Y. C. Huang, Niu, Yang, & Jinn, 2016), plays a role in inhibition of disease resistance by HTS(Mang et al., 2012). Despite the distinct nature of pathogen infection and HTS and their different modes of perception by plant cells(Jones & Dangl, 2006; Mittler, Finka, & Goloubinoff, 2012), signaling initiated by HTS and pathogen attack share components such as reactive oxygen species (ROS), phytohormones including JA and salicylic acid (SA), and transcription factors such as WRKY33(Li, Fu, Chen, Huang, & Yu, 2011; J. Liu, Feng, Li, & He, 2015; S. Liu, Kracher, Ziegler, Birkenbihl, & Somssich, 2015). However, how plants coordinately respond to HTS and pathogen attacks remain elusive.
As plant response to various stresses are largely regulated at transcriptional level mediated by transcription factors(TFs)(Moore, Loake, & Spoel, 2011). NAC [No apical meristem (NAM), Arabidopsis transcription activation factor (ATAF), Cup-shaped cotyledon (CUC)] constitute one of the largest plant TF families, they generally contain a well conserved N-terminal NAC domain and a diversified C-terminal transcription regulatory region, and were classified comprehensively into eight subfamilies(Puranik, Sahu, Srivastava, & Prasad, 2012). NAC transcription factors have been implicated in the regulation of plant response to stress conditions by binding specific recognition site [CGT(G/A)] in their target genes(L. Fang et al., 2016; Khedia, Agarwal, & Agarwal, 2018). The stress response related NACs fall into one subgroup(Y. Fang, You, Xie, Xie, & Xiong, 2008; Nakashima, Takasaki, Mizoi, Shinozaki, & Yamaguchi-Shinozaki, 2012; Negi, Tak, & Ganapathi, 2018), these stress response related NACs might be regulated at multiple levels including transcriptional, post-transcriptional and post-translational level (W. Huang et al., 2013; Puranik et al., 2012; Tran et al., 2004). In addition, a single NAC TF might act as convergent node of plant response to different stress conditions(McGrann et al., 2015). However, the role of these NAC TFs and how they operate in the coordination of different plant biological processes currently remains poorly understood.
Pepper (Capsicum annuum ) is a solanaceous vegetable of great economic importance worldwide. Bacterial wilt caused by root infection of R. solanacearum , a soil borne pathogen with extremely versatile lifestyle (Jiang et al., 2017; Mansfield et al., 2012), is one of the most frequently occurred diseases(Du et al., 2017). The bacterium attacks pepper plants by penetrating the root system, proliferating and spreading through xylem vessels, causing the disruption of the plant vascular system and eventual plant wilting(Digonnet et al., 2012; Mansfield et al., 2012; Turner et al., 2009). HTS is another important abotic stress frequently encountered by pepper in tropical and subtropical climates usually cause retard in pepper growth and development. To survive these stresses, the response of pepper to these stresses and growth should be appropriately coordinated. However, how pepper coordinately respond to RSI and HTS currently remain elusive. In the present study, we found that CaNAC2c play a crucial role in the tradeoffs among pepper growth and its response to RSI and HTS.