## 1 Introduction  
The six major types of tea in China are distinguished by their different manufacturing methods, among which oolong tea has the most complicated procedure. Due to its unique history and culture, abundant germplasm resources, and exquisite processing technology, oolong tea is highly fragrant with a mellow taste, and it is deeply favored by consumers [1; 2]. Aroma is one of the key factors determining the quality of tea [3]. The aromatic quality of oolong tea is affected by tea varieties, growth environments, cultivation conditions, and, more importantly, the multiple stress treatments of the fresh leaves during the post-harvest procedure [4; 5; 6]. Most volatile organic compounds (VOCs) form and accumulate during the post-harvest procedure of oolong tea [7]. The endogenous enzyme biochemical reaction caused by turnover and the physical-chemical reaction caused by fermentation as well as drying are two of the main reasons for VOC formation and accumulation during the post-harvest process of oolong tea [8; 9]. It is noteworthy that turnover is the core method for forming the characteristic floral and fruity aroma quality of oolong tea [10]. The formation of oolong tea's aroma relies on four metabolic pathways: the terpene pathway, the fatty acid pathway, the benzene ring/phenylpropane pathway, and the carotenoid pathway [11; 12]. Among these, phenylpropanoids/benzenoids, the second most common volatile components in the plant kingdom, play a vital role in determining the aroma of tea. L-phe is an important product in the shikimic acid metabolism pathway. There are three main branches that form VBs/VPs, taking L-phe as a precursor under enzymatic reactions. Firstly, under the reaction of phenylalanine lyase (PAL), the intermediate product trans-cinnamic acid forms, followed by VBs such as benzaldehyde, benzyl alcohol, benzoic acid, and salicylic acid, which are generated through enzymatic and non-enzymatic reactions [13]. Secondly, phenylacetaldehyde synthase (PAAS) directly reacts with L-phe to form VPs, including phenylacetaldehyde, phenylethanol, and phenylethyl ester [14]. Thirdly, L-phe can also participate in the formation of VBs/VPs after forming phenylpyruvate acid (PA) under the reaction of aromatic amino acid transaminase (AAAT), which has been confirmed in watermlemon, rose, camellia, and some other horticultural crops [15; 16; 17]. [PERSON] et al. (2019) reported that PA was obtained from L-phe under the catalysis of _CsAAAT_ using isotope tracer technology [18]. In addition, the _CsAAAT_ and _CsAAAT_2 genes, with a high catalytic efficiency for L-phe and tyrosine, were screened for the first time. Furthermore, in terms of the quality of oolong tea products, an increasing amount of research points to the contribution of VBs/VPs in oolong tea's flavor quality. Previous studies found that VBs/VPs, including indole [19], benzaldehyde and benzyl alcohol [20; 21], phenylethanol and phenylacetaldehyde [22; 23], and hexyl benzoate and cis-3-hexenyl benzoate [24; 25], were formed during the post-harvest process of oolong tea, which would eventually contribute to the aromatic quality of oolong tea (Figure 1). However, the specific VB/VP components that contribute to the aromatic quality of oolong tea remain unclear. Compared to previous studies on PAL and PAAS branches, the AAAT branch has received less attention. Even less is known about the transcription mechanism of _CsAAAT_ genes and its influence on the dynamic changes in VBs/VPs during the post-harvest process of oolong tea. Therefore, in this study, oolong tea manufacturing process samples were utilized as materials. The metabolic profiles of the VBs/VPs were constructed, and then based on a tea genome database (CSS) and transcriptome database, the transcripts of key _CsAAAT_ genes related to VB/VP changes were screened. The purpose  
Figure 1: Three pathways of VB/VP formation in tea plants [18; 26; 27; 28; 29; 30; 31; 32; 33]. Potential metabolic pathways for converting L-phenylalanine into VBs/VPs in plants.