柑橘黄龙病相关水杨酸羧基甲基转移酶基因CsSAMT-1的克隆与表达分析

为研究水杨酸羧基甲基转移酶(Salicylic acid carboxyl methyltransferase,SAMT)在柑橘防御黄龙病(Huanglongbing,HLB)中的作用,克隆获得Cs SAMT~(-1)基因,并以易感HLB锦橙和耐HLB酸柚为试材进行基因表达分析。q RT-PCR结果表明,易感病锦橙中CsSAMT~(-1)在感染HLB后上调表达,且在叶脉中的表达量显著高于叶肉;而耐病酸柚中CsSAMT~(-1)呈组成型表达。外源水杨酸(SA)和茉莉酸甲酯(MeJA)处理锦橙和酸柚,均可诱导CsSAMT~(-1)上调表达。HLB侵染前,耐病酸柚叶脉中SA和水杨酸甲酯(MeSA)含量分别为11.85和18.18 ng·g~(-1),显著高于锦橙(0.82和0.01 ng·g~(-1));HLB侵染后,锦橙中SA和MeSA含量明显上升,酸柚中SA含量明显下降,MeSA含量基本保持原有水平。研究表明,Cs SAMT~(-1)可能通过调节SA和Me SA信号分子转换来增强对柑橘黄龙病的抗性。

Cloning and Expression Analysis of HLB-associated Salicylic Acid Carboxyl Methyltransferase Gene CsSAMT-1 in Citrus

Salicylic acid（SA）plays a pivotal role in plant resistance to pathogens. Salicylic acid carboxyl methyltransferase（SAMT）is an enzyme for catalyzing the formation of methyl salicylate（MeSA）from SA. Here，we cloned a SAMT gene named as CsSAMT-1，which was associated with Huanglongbing（HLB）infection. In HLB-susceptible Jincheng orange（Citrus sinensis Osbeck），the expression level of CsSAMT-1 was highly induced by HLB infection，in contrast to the constitutive expression of CsSAMT-1 in a HLB-resistant variety，sour pomelo（C. grandis Osbeck）. CsSAMT-1 was also induced by SA and methyl jasmonate（MeJA）in both Jincheng orange and sour pomelo. Moreover，the expression level of CsSAMT-1 in the vein was higher than that in the mesophyll. The contents of SA and MeSA in the vein of sour pomelo were 11.85 and 18.18 ng ? g-1，respectively，which were significantly higher than that（0.82 and 0.0072 ng ? g-1）in the vein of Jingcheng orange. After HLB infection，the contents of both SA and MeSA were markedly increased in Jincheng orange；while in sour pomelo，SA content was decreased and MeSA remained unchanged. Taken together，our results suggest that CsSAMT-1 may confer resistance to HLB through mediating the conversion of SA and MeSA in citrus.