Abstract
WRKY transcription factors (WRKY TFs) are one of the largest protein families in plants, and most of them play vital roles in response to biotic and abiotic stresses by regulating related signaling pathways. In this study, we isolated two WRKY TF genes PtrWRKY18 and PtrWRKY35 from Populus trichocarpa and overexpressed them in Arabidopsis. Expression pattern analyses showed that PtrWRKY18 and PtrWRKY35 respond to salicylic acid (SA), methyl JA (MeJA), abscisic acid (ABA), B. cinereal, and P. syringae treatment. The transgenic plants conferred higher B. cinerea tolerance than wild-type (WT) plants, and real-time quantitative (qRT)-PCR assays showed that PR3 and PDF1.2 had higher expression levels in transgenic plants, which was consistent with their tolerance to B. cinereal. The transgenic plants showed lower P. syringae tolerance than WT plants, and qRT-PCR analysis (PR1, PR2, and NPR1) also corresponded to this phenotype. Germination rate and root analysis showed that the transgenic plants are less sensitive to ABA, which leads to the reduced tolerance to osmotic stress and the increase of the death ratio and stomatal aperture. Compared with WT plants, a series of ABA-related genes (RD29A, ABO3, ABI4, ABI5, and DREB1A) were significantly down-regulated in PtrWRKY18 and PtrWRKY35 overexpression plants. All of these results demonstrated that the two WRKY TFs are multifunctional transcription factors in plant resistance.
Highlights
Thanks to their sessile lifestyle, high plants have to face various biotic and abiotic stresses [1]
The signals that participate in plant responses are usually divided into two types: fast-moving signals that react within minutes, such as methyl JA (MeJA) or methyl SA (MeSA), and slow-moving signals that need several hours to transport and respond to changes, such as jasmonic acid (JA), salicylic acid (SA), or azelaic acid [3]
The expression of PtrWRKY18 and PtrWRKY35 was significantly induced by P. syringae and B. cinerea, two pathogen species, as well as by SA and JA, two hormones involved in pathogen resistance (Figure 1A)
Summary
Thanks to their sessile lifestyle, high plants have to face various biotic and abiotic stresses [1]. To cope with these challenges, plants have evolved sophisticated mechanisms to perceive these environmental stresses and respond optimally [2]. Recognition and transduction of stress signals to activate plant responses and regulation of stress-resistant genes are the key steps for enabling stress tolerance in plants. The stress-resistant genes are mainly induced at the transcriptional level, and many transcription factor (TF) families such as WRKY, AP2 (APETALA2)/ERF (ethylene responsive factor), and NAC (NAM, ATAF1/2, CUC1/2) play crucial roles in activating the expression of many stress-resistant genes during diverse biotic and abiotic stress responses [4]
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