Trainotti L, Spolaore S, Pavanello A, Baldan B, Casadoro G
Dipartimento di Biologia, Università di Padova, Italy.
Plant Mol Biol. 1999 May;40(2):323-32. doi: 10.1023/a:1006299821980.
Two full-length cDNA clones (faEG1 and faEG3, respectively) have been isolated by screening a cDNA library representing transcripts from red strawberry fruits. Southern blot analysis of genomic DNA suggests that the strawberry endo-beta-1,4-glucanases (EGases) are encoded by a multigene family. The cognate genes are predominantly expressed during the ripening process proper, although, in the case of faEG3, some expression has also been observed in large green fruits and, at low amounts, in young vegetative green tissues. In agreement with other ripening-related genes in strawberry, also the expression of faEG1 and faEG3 is down-regulated by treatment with an auxin analogue (1-naphthaleneacetic acid, NAA). Differences in temporal expression of the two EGase genes in fruits are not accompanied by differences in spatial expression. The pattern of expression and the sequence characteristics of the two polypeptides suggest that the two strawberry EGases operate in a synergistic and coordinate manner. The protein encoded by faEG1 looks like one of the usual higher-plant EGases (average molecular mass of 54 kDa), while the protein encoded by faEG3 has a greater deduced molecular mass (about 68 kDa) due to the presence of an extra peptide of about 130 amino acids at the C-terminus. Such unusual peptide shows some features also found in microbial cellulases and contains a putative cellulose-binding domain. We propose that the faEG3-encoded EGase might especially hydrolyse the xyloglucans coating the cellulose microfibrils, thus rendering the cell wall more susceptible to the subsequent hydrolytic activity of the faEG1-encoded EGase.
通过筛选一个代表红草莓果实转录本的cDNA文库，已分离出两个全长cDNA克隆（分别为faEG1和faEG3）。基因组DNA的Southern印迹分析表明，草莓内切β-1,4-葡聚糖酶（EGases）由一个多基因家族编码。同源基因主要在果实成熟过程中表达，不过，就faEG3而言，在大的绿色果实中也观察到了一些表达，并且在幼嫩的营养绿色组织中表达量较低。与草莓中其他与成熟相关的基因一致，用生长素类似物（1-萘乙酸，NAA）处理也会下调faEG1和faEG3的表达。果实中两个EGase基因在时间表达上的差异并未伴随着空间表达上的差异。这两个多肽的表达模式和序列特征表明，这两种草莓EGases以协同和协调的方式发挥作用。faEG1编码的蛋白质看起来像常见的高等植物EGases之一（平均分子量为54 kDa），而faEG3编码的蛋白质由于在C端存在一个约130个氨基酸的额外肽段，其推导分子量更大（约68 kDa）。这种不寻常的肽段也具有一些在微生物纤维素酶中发现的特征，并包含一个假定的纤维素结合结构域。我们推测，faEG3编码的EGase可能特别水解包裹纤维素微纤丝的木葡聚糖，从而使细胞壁更容易受到faEG1编码的EGase随后的水解活性作用。
