Developmental Localization and Methylesterification of Pectin Epitopes during Somatic Embryogenesis of Banana (Musa spp. AAA)

Abstract

BackgroundThe plant cell walls play an important role in somatic embryogenesis and plant development. Pectins are major chemical components of primary cell walls while homogalacturonan (HG) is the most abundant pectin polysaccharide. Developmental regulation of HG methyl-esterification degree is important for cell adhesion, division and expansion, and in general for proper organ and plant development.Methodology/Principal FindingsDevelopmental localization of pectic homogalacturonan (HG) epitopes and the (1→4)-β-D-galactan epitope of rhamnogalacturonan I (RG-I) and degree of pectin methyl-esterification (DM) were studied during somatic embryogenesis of banana (Musa spp. AAA). Histological analysis documented all major developmental stages including embryogenic cells (ECs), pre-globular, globular, pear-shaped and cotyledonary somatic embryos. Histochemical staining of extracellularly secreted pectins with ruthenium red showed the most intense staining at the surface of pre-globular, globular and pear-shaped somatic embryos. Biochemical analysis revealed developmental regulation of galacturonic acid content and DM in diverse embryogenic stages. Immunodots and immunolabeling on tissue sections revealed developmental regulation of highly methyl-esterified HG epitopes recognized by JIM7 and LM20 antibodies during somatic embryogenesis. Cell walls of pre-globular/globular and late-stage embryos contained both low methyl-esterified HG epitopes as well as partially and highly methyl-esterified ones. Extracellular matrix which covered surface of early developing embryos contained pectin epitopes recognized by 2F4, LM18, JIM5, JIM7 and LM5 antibodies. De-esterification of cell wall pectins by NaOH caused a decrease or an elimination of immunolabeling in the case of highly methyl-esterified HG epitopes. However, immunolabeling of some low methyl-esterified epitopes appeared stronger after this base treatment.Conclusions/SignificanceThese data suggest that both low- and highly-methyl-esterified HG epitopes are developmentally regulated in diverse embryogenic stages during somatic embryogenesis. This study provides new information about pectin composition, HG methyl-esterification and developmental localization of pectin epitopes during somatic embryogenesis of banana.

Arabinogalactan-protein and pectin epitopes in relation to an extracellular matrix surface network and somatic embryogenesis and callogenesis in Trifolium nigrescens Viv.

“…Pectin polymers have been already identified in the ECMSN of embryogenic cultures of carrot (Iwai et al 1999), chicory (Chapman et al 2000b), coconut (Verdeil et al 2001), and banana . In addition, conspicuous differences in pectic composition of the ECMSN coating embryogenic/organogenic and non-regenerative callus domains were reported (Iwai et al 1999;Konieczny et al 2007;Pilarska et al 2007;Xu et al 2011). The results obtained in our study also indicate a tissue-specific composition of the ECMSN: JIM5-reactive HG was detected in the ECMSN over callus surface but not on the surface of somatic embryos.…”

“…The results obtained in our study also indicate a tissue-specific composition of the ECMSN: JIM5-reactive HG was detected in the ECMSN over callus surface but not on the surface of somatic embryos. In tissues cultured in vitro, Popielarska-Konieczna et al (2008) and Xu et al (2011) localized the JIM5 epitope to the ECMSN coating non-dividing and relatively large parenchyma cells of callus. Noticeably, the cells of T. nigrescens that carried the JIM5 epitope were loosely attached which suggests a relationship between location of low methylesterified HG and cell separation in cultured callus.…”

Extracellular matrix surface network is associated with non-morphogenic calli of Helianthus tuberosus cv. Albik produced from various explants

“…However, in the present studies, in spite of the occurrence of ECMSN the calli were not morphogenetic. The extracellular layer covering callus cells, which is not involved in the regeneration process, has previously been reported during androgenesis in wheat [34], somatic embryogenesis in banana [35] and clover cultures [36]. The role of ECMSN cannot be generalized but it is evident that it is formed on the surface of cultured in vitro tissues regardless of its morphogenetic competence.…”

SALT-OVERLY SENSITIVE5 Mediates Arabidopsis Seed Coat Mucilage Adherence and Organization through Pectins

“…The specificities of the primary antibodies JIM5 and JIM7 (CarboSource) have been extensively described (Liners et al, 1989;Knox et al, 1990;Knox, 1997;Willats et al, 2001aWillats et al, , 2001bWillats et al, , 2001cMacquet et al, 2007a;Pattathil et al, 2010;Xu et al, 2011). JIM13, MAC207, JIM8, and CCRC-M7 (CarboSource) have also been previously described (Bradley et al, 1988;Pennell et al, 1989Pennell et al, , 1991Knox et al, 1991;Puhlmann et al, 1994;Yates and Knox, 1994;Steffan et al, 1995;Yates et al, 1996;Majewska-Sawka and Nothnagel, 2000;Pattathil et al, 2010).…”