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.