Isolation of a Polygalacturonase Gene from Citrus sinensis Fruit and Its Expression Relative to Fruit Mastication Trait, Fruit Development, and Calcium or Boron Treatments

Abstract

Polygalacturonase (PG) plays a significant role in pectin solubilization and depolymerization in vivo and is involved in numerous plant developmental processes. In this study, a polygalacturonase gene (CitPG, EF185420) was isolated from Citrus sinensis. It is 1,686 bp with a putative open reading frame of 1,338 bp encoding 445 amino acids. Phylogenetic analysis showed that CitPG belongs to clade B which includes PGs expressed in fruits or dehiscence zones. CitPG expression profiles during fruit ripening were compared between two pairs of varieties which differ in their mastication traits: C. sinensis cv. Fengjiewancheng (FJWC) vs. C. sinensis cv. Fengjie 72-1 (FJ72-1) and Citrus reticulata cv. Kinokuni (NM) vs. C. reticulata cv. Miguang (MG), in which the mastication trait of "FJWC" and "NM" are inferior to their respective partner cultivars. Results indicated that the CitPG transcript level was significantly lower in the inferior mastication variety at the late ripening stage or at all ripening stages. Calcium or boron treatment resulted in a significant reduction in CitPG transcription level in fruit pulp at harvest time (235 days after anthesis). This was accompanied by an increase in protopectin content. In addition, the mRNA level of CitPG in the fruit peel and pulp increased during the fruit's rapid cell enlargement stage and was inversely correlated with protopectin levels. These results suggest that CitPG is associated with the favorable enhancement of the fruit mastication trait and is involved in dissolving the protopectin during cell enlargement.

Soil application of calcium and magnesium fertilizer influences the fruit pulp mastication characteristics of Nanfeng tangerine (Citrus reticulata Blanco cv. Kinokuni)

“…The yield and cultivated area of NM have increased in recent decades; however there is a big challenge now due to the inferior mastication characteristics of the fruit, which has decreased the market competitiveness of NM. The inferior texture quality of citrus fruit pulp has been depicted as "non-melting" (Deng, 2008), which is characterized by a coarse feeling in the mouth while eating with rough fiber residue after patiently chewing the fruit segments before swallowing (Liu et al, 2011). Moreover, this texture quality can be quantitatively evaluated using a texture analyser to measure the shear force required to slice through the fruit segment (Wei et al, 2014).…”

“…The texture of fruit can be modulated by regulatory genes in many types of fleshy fruits (Seymour et al, 2002;Liu et al, 2011).…”

Identification of Ethylene-Responsive Genes in Ethrel-Treated Shoot Apices of Cucumber by Suppression Subtractive Hybridization

“…BLASTn analysis of tomato PG promoter revealed sequence homology (between 80% and 86% sequence identities) to various regions of the 1-aminocylopropane-1-carboxylate (ACC) synthase-encoding gene (Joann et al 2009). The gene expression of PG gene (CitPG) from Citrus sinensis fruit was significantly lower in the inferior mastication variety at the late ripening stage (Liu et al 2011). This suggested that CitPG is associated with the favorable enhancement of the fruit mastication trait and is involved in dissolving the protopectin during cell enlargement.…”

A Novel Non-wounding Transient Expression Assay for Cereals Mediated by Agrobacterium tumefaciens

“…Furthermore, gene interrelationships or "gene webs" can be studied under different stress treatments with the aid of microarrays. AmTEA can be easily adapted to evaluate promoters and genes in dicots other than Arabidopsis, including plants with fruits such as citrus (Liu et al 2011) and tomato. The small size and tender nature of the young plants offer the possibility of automation of this method for high throughput screening of promoters and genes.…”