# Cloning and Functional Identification of _Sipg49_ in _Solanum Lyopersicum_  
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1 Collaborative Innovation Center for Efficient and Green Production of Agriculture in Mountainous Areas of Zhejiang Province, College of Horticulture Science, Zhejiang A&F University, Hangzhou 311300, China; [EMAIL_ADDRESS] (W.L.); [EMAIL_ADDRESS] (L.X.); [EMAIL_ADDRESS] (R.X.); [EMAIL_ADDRESS] (Y.S.); [EMAIL_ADDRESS] (Z.Z.)  
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1 Collaborative Innovation Center for Efficient and Green Production of Agriculture in Mountainous Areas of Zhejiang Province, College of Horticulture Science, Zhejiang A&F University, Hangzhou 311300, China; [EMAIL_ADDRESS] (W.L.); [EMAIL_ADDRESS] (L.X.); [EMAIL_ADDRESS] (R.X.); [EMAIL_ADDRESS] (Y.S.); [EMAIL_ADDRESS] (Z.Z.)  
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PGs are one of the largest hydrolase families in plants [22], and contain four common conserved domains (domains I-IV) [23]. Based on their modes of action, PGs can be further divided into three different types: endo-PGs, exo-PGs, and rhamnose-PGs [24; 25].  
PGs are needed to degrade polygalacturonic acid and promote pectin degradation, and are of great significance to plant growth and development [6]. PGs are involved in plant morphogenesis [26; 27], pollen development [28; 29], organ shedding [30], fruit ripening [1], and other processes in plants [31]. Arabidopsis ATPG45 regulates leaf shape by affecting the proliferation and expansion of epidermal cells [26; 27]. The absence of BclMF16 in _Brassica campestris_ leads to the loss of pollen inner wall and inclusions [32]. PGZAT is a PG gene expressed in leaf abscission zones and functions in the cell separation process [33].  
The relationship between PGs and fruit development has always been a research hotspot in this field, mainly focusing on species that use fruits as edible organs, such as Citrus sinensis, apples, and strawberries [34; 35; 36]. Strawberry lines that silence FaPG1 have soluble pectin of a higher molecular weight and show more supramolecular pectin aggregates than controls, indicating that FaPG1 plays a role in promoting the degradation of pectin, thereby accelerating fruit ripening [37]. Studies have found that mature fruits with inhibited MDPG1 expression in apples have higher intercellular adhesion, weakened subcutaneous cell expansion, and denser cells [38]. In addition, it was also verified that PGs could promote fruit softening by hydrolyzing pectin in cell walls of bananas, kiwis, and pears [39; 40; 41]. A transformed tomato with an antisense PG gene resulted in hardened fruit texture and lengthened shelf life [42]. Interestingly, although the mutation of tomato PG2A affects fruit color and weight, it has no effect on fruit softening [8], which may be due to the redundancy of the PGs in tomato plants. In a recent study, we characterized 54 PG members from tomato plants and found that multiple PG genes were highly expressed during fruit ripening [18]. Intriguingly, _Solanum Lyopersicum_ POLYGALACTRONASE49 (SIFG49) was highly expressed in the pericarp, suggesting that it may be critical to fruit softening. However, its biological functions remain unclear.  
Here, the full length of a tomato PG gene (SIPG49) cDNA was cloned and bioinformatically analyzed. The expression pattern of SIPG49 was further confirmed by qRT-PCR. Moreover, the bio-functions of SIPG49 were further identified through subcellular localization and enzymatic activity analysis in vitro. This study could be valuable for providing a reliable experimental basis for future PG research and developing new tomato varieties with enhanced tolerance to fruit softening or long shelf life.