Key Laboratory of Protected Horticulture of Education Ministry and Liaoning Province, College of Horticulture, Shenyang Agricultural University, National & Local Joint Engineering Research Center of Northern Horticultural Facilities Design & Application Technology (Liaoning), Shenyang, 110866, Liaoning, People's Republic of China.
Vegetable Research Institute, Liaoning Academy of Agricultural Sciences, Shenyang, 110161, Liaoning, People's Republic of China.
BMC Plant Biol. 2021 Feb 8;21(1):83. doi: 10.1186/s12870-021-02869-y.
Cinnamyl alcohol dehydrogenase (CAD) is an important enzyme functions at the last step in lignin monomer synthesis pathway. Our previous work found that drought induced the expressions of CmCAD genes and promoted lignin biosynthesis in melon stems.
Here we studied the effects of abscisic acid (ABA), hydrogen peroxide (HO) and jasmonic acid (JA) to CmCADs under drought stress. Results discovered that drought-induced ABA, HO and MeJA were prevented efficiently from increasing in melon stems pretreated with fluridone (Flu, ABA inhibitor), imidazole (Imi, HO scavenger) and ibuprofen (Ibu, JA inhibitor). ABA and HO are involved in the positive regulations to CmCAD1, 2, 3, and 5, and JA is involved in the positive regulations to CmCAD2, 3, and 5. According to the expression profiles of lignin biosynthesis genes, ABA, HO and MeJA all showed positive regulations to CmPAL2-like, CmPOD1-like, CmPOD2-like and CmLAC4-like. In addition, positive regulations were also observed with ABA to CmPAL1-like, CmC4H and CmCOMT, with HO to CmPAL1-like, CmC4H, CmCCR and CmLAC17-like, and with JA to CmCCR, CmCOMT, CmLAC11-like and CmLAC17-like. As expected, the signal molecules positively regulated CAD activity and lignin biosynthesis under drought stress. Promoter::GUS assays not only further confirmed the regulations of the signal molecules to CmCAD1~3, but also revealed the important role of CmCAD3 in lignin synthesis due to the strongest staining of CmCAD3 promoter::GUS.
CmCADs but CmCAD4 are positively regulated by ABA, HO and JA under drought stress and participate in lignin synthesis.
肉桂醇脱氢酶（CAD）是木质素单体合成途径中最后一步的重要酶。我们之前的工作发现干旱诱导了甜瓜茎中 CmCAD 基因的表达，并促进了木质素的生物合成。
在这里，我们研究了脱落酸（ABA）、过氧化氢（HO）和茉莉酸（JA）在干旱胁迫下对 CmCADs 的影响。结果发现，用氟啶酮（Flu，ABA 抑制剂）、咪唑（Imi，HO 清除剂）和布洛芬（Ibu，JA 抑制剂）预处理甜瓜茎可有效阻止干旱诱导的 ABA、HO 和 MeJA 的增加。ABA 和 HO 参与对 CmCAD1、2、3 和 5 的正向调控，而 JA 参与对 CmCAD2、3 和 5 的正向调控。根据木质素生物合成基因的表达谱，ABA、HO 和 MeJA 均对 CmPAL2-like、CmPOD1-like、CmPOD2-like 和 CmLAC4-like 表现出正向调控。此外，ABA 对 CmPAL1-like、CmC4H 和 CmCOMT 也表现出正向调控，HO 对 CmPAL1-like、CmC4H、CmCCR 和 CmLAC17-like 也表现出正向调控，JA 对 CmCCR、CmCOMT、CmLAC11-like 和 CmLAC17-like 也表现出正向调控。正如预期的那样，信号分子在干旱胁迫下正向调控 CAD 活性和木质素生物合成。启动子::GUS 分析不仅进一步证实了信号分子对 CmCAD1~3 的调控，还揭示了 CmCAD3 在木质素合成中的重要作用，因为 CmCAD3 启动子::GUS 的染色最强。
CmCADs（但不是 CmCAD4）在干旱胁迫下被 ABA、HO 和 JA 正向调控，并参与木质素的合成。
