Departamento de Botânica-IB-USP, 277, 05508-900, São Paulo, SP, Brazil.
J Exp Bot. 2013 May;64(8):2449-66. doi: 10.1093/jxb/ert106. Epub 2013 Apr 18.
Pectin is a main component of the plant cell wall and is the most complex family of polysaccharides in nature. Its composition is essential for the normal growth and morphology pattern, as demonstrated by pectin-defective mutant phenotypes. Besides this basic role in plant physiology, in tomato, pectin structure contributes to very important quality traits such as fruit firmness. Sixty-seven different enzymatic activities have been suggested to be required for pectin biosynthesis, but only a few genes have been identified and studied so far. This study characterized the tomato galacturonosyltransferase (GAUT) family and performed a detailed functional study of the GAUT4 gene. The tomato genome harbours all genes orthologous to those described previously in Arabidopsis thaliana, and a transcriptional profile revealed that the GAUT4 gene was expressed at higher levels in developing organs. GAUT4-silenced tomato plants exhibited an increment in vegetative biomass associated with palisade parenchyma enlargement. Silenced fruits showed an altered pectin composition and accumulated less starch along with a reduced amount of pectin, which coincided with an increase in firmness. Moreover, the harvest index was dramatically reduced as a consequence of the reduction in the fruit weight and number. Altogether, these results suggest that, beyond its role in pectin biosynthesis, GAUT4 interferes with carbon metabolism, partitioning, and allocation. Hence, this cell-wall-related gene seems to be key in determining plant growth and fruit production in tomato.
果胶是植物细胞壁的主要成分，是自然界中最复杂的多糖家族。果胶缺陷型突变体表型表明，其组成对植物的正常生长和形态模式至关重要。除了在植物生理学中的基本作用外，果胶结构在番茄中对果实硬度等非常重要的品质特性也有贡献。已有 67 种不同的酶活性被认为是果胶生物合成所必需的，但迄今为止，只有少数基因被鉴定和研究过。本研究对番茄半乳糖醛酸转移酶（GAUT）家族进行了特征描述，并对 GAUT4 基因进行了详细的功能研究。番茄基因组包含了与先前在拟南芥中描述的同源基因，转录谱显示 GAUT4 基因在发育器官中表达水平更高。沉默 GAUT4 的番茄植株表现出生长旺盛，栅栏薄壁组织增大。沉默的果实表现出果胶组成的改变，淀粉积累减少，果胶含量降低，硬度增加。此外，由于果实重量和数量的减少，收获指数显著降低。总之，这些结果表明，除了在果胶生物合成中的作用外，GAUT4 还干扰了碳代谢、分配和分配。因此，这个与细胞壁相关的基因似乎是决定番茄生长和果实产量的关键。
