Cell Wall Mechanical Strength Research Articles

RsERF40 contributes to cold stress tolerance and cell expansion of taproot in radish (Raphanus sativus L.).

The growth and development of taproots are inhibited by cold stress in radish (Raphanus sativus L.). Ethylene-responsive element binding factors (ERF) are key participators in the cold stress response and growth regulation of plants. However, the function of ERF genes in cold tolerance and root development in radish remains elusive. Here, we showed that the secondary growth of radish taproots was inhibited by cold stress. Comparative transcriptome analysis demonstrated that the RsERF40 gene is an important regulator of the cold stress response and root growth regulation. The cold tolerance of transgenic Arabidopsis plants overexpressing the RsERF40 gene was significantly improved. Overexpressing RsERF40 in the cold-sensitive radish genotype and silencing RsERF40 in the cold-tolerant radish genotype indicated that RsERF40 was beneficial for alleviating oxidative damage under cold stress in radish. Transgenic Arabidopsis seedlings showed an increase in the elongation and radial growth of dark-grown roots. RT-qPCR analysis showed that the expression of the cold-related genes (CORs) RsCOR78 and RsCOR413PM1 and the cell wall strengthening-related genes RsCESA6 and RsEXPB3 was upregulated in transgenic Arabidopsis seedlings. Yeast one-hybrid (Y1H) and dual-luciferase reporter assays (DLA) revealed that RsERF40 directly regulates RsCOR78, RsCOR413PM1, RsCESA6 and RsEXPB3 expression, illustrating that RsERF40 enhances cold tolerance and taproot growth by modulating osmotic adjustment and cell wall mechanical strength in radish. In this study, the RsERF40-regulon was firstly found to be a new cold response pathway independent of the CBF-COR pathway conferring cold stress tolerance with increasing radish taproot growth. These results provided novel insight into the molecular mechanism underlying cold stress response and would facilitate the genetic improvement of cold tolerance in radish and other root vegetable crops.

Tissue-specific pectin methylesterification and pectin methylesterase activities play a role in lettuce seed germination

Cell wall mechanical strength is partially controlled by the degree of pectin methylesterification that is mediated through the action of pectin methylesterases (PMEs). Changes in cell wall mechanical strength are involved in the endosperm cap weakening and radicle elongation growth during the germination of some endospermic seeds. However, little is known about the roles of the status of pectin methylesterification and PME activities during seed germination, especially in lettuce, a traditional model plant for seed germination research. In the present study, we demonstrated that the rupture of lettuce endosperm cap during seed germination was caused by cell rupture, not by cell separation as formerly reported in other species. Next, we investigated the status of pectin methylesterification of the endosperm cap and radicle during germination, using immunolabeling by specific monoclonal antibodies against methyl-esterified pectins and calcium bridges. We also analyzed the expression patterns of PME activities and an encoding gene LsPME/PMEI51 in the endosperm cap and radicle. It was found that cell walls of the endosperm cap comprise more methyl-esterified pectins than radicle, while PME activities and the abundance of LsPME/PMEI51 transcripts in the endosperm cap are lower than those in the radicle. In addition, the status of pectin methylesterification and PME expression patterns changed during seed germination. Low PME activities and high pectin methylesterification in the endosperm cap is hypothesized to be the reason of why endosperm does not rupture by cell separation. It is concluded that tissue-specific pectin methylesterification and PME activities play a role in lettuce seed germination.

Pectin methyl esterases and pectins in normal and hyperhydric shoots of carnation cultured in vitro

Control and hyperhydric micropropagated plantlets from three carnation cultivars have been used to study their pectin composition and the activity of pectin methyl esterases (PMEs; EC 3.1.1.11). Pectins are a highly heterogeneous group of polymers that contribute to cell adhesion, cell wall architecture, and cell wall mechanical strength. Pectins control cell wall porosity and cell wall ionic status and are implicated in intercellular space development. The degree of esterification of pectins is controlled by the activity of cell wall PMEs; their different actions can affect the properties of the cell wall, which have been considered important with respect to controlling the development of hyperhydricity. The total pectins of hyperhydric leaves of the three varieties were significantly reduced in comparison with controls. The pectate fraction was significantly increased in hyperhydric leaves of all varieties while soluble pectins and protopectins were significantly lower. The PME activity of hyperhydric leaves was higher (4–10 times) compared to controls of the three varieties. Isoelectric focusing of PME isozymes revealed the presence of three isoforms; neutral PME activity was the major isozyme in control and hyperhydric leaves of the three varieties, whilst a decrease in the activity of the acidic isoforms was observed in hyperhydric leaves. The different PME activities could regulate some of the structural changes related to hyperhydricity in micropropagated carnation plants.