cDNA Cloning of a Novel Lectin-Like Xylem Sap Protein and Its Root-Specific Expression in Cucumber

Abstract

A novel cDNA encoding a major 30-kDa protein in xylem sap of cucumber Cucumis sativus (XSP30) was homologous to the B chains of galactose-binding lectins such as ricin and abrin. XSP30 gene was specifically expressed in roots, and XSP30 was immunologically detected only in the xylem sap, but not in any organs.

Root-derived CLE glycopeptides control nodulation by direct binding to HAR1 receptor kinase

“…However, we show here that the xylem also transports peptide signals that mediate systemic responses in plants. It remains to be elucidated whether the xylem loading of [Ara 3 ]CLE-RS2 glycopeptide is a passive (nonselective) or an active (selective) process; however, some known xylem proteins appear to be specifically expressed in roots suggesting the presence of a system for secretion into the xylem from the root cells 30,31 . How [Ara 3 ]CLE-RS2 glycopeptide is loaded into root xylem is a topic of great interest for future study.…”

Evolution of Plant Ribosome-Inactivating Proteins

“…Proteins consisting exclusively of polypeptides equivalent to the B-chain of type 2 RIPs have been isolated from several Sambucus species (e.g., fruit lectin SNA-IV) (Girbés et al 2004;Van Damme et al 1997b) and from cucumber (C. sativus) roots (XSP30) (Masuda et al 1999). Moreover, it seems quite likely that several lectins previously isolated from different Euphorbia species are built up of B-chains only In spite of the tremendous amount of (multidisciplinary) research devoted to ricin and related proteins, the molecular evolution and especially the evolutionary origin of type 2 RIPs is still far from understood.…”

Possible Involvement of Leaf Gibberellins in the Clock-Controlled Expression of XSP30, a Gene Encoding a Xylem Sap Lectin, in Cucumber Roots

“…Interestingly, the roots control aspects of the development of aerial organs, possibly acting via growth-related compounds in the xylem sap (Kinet et al, 1993;Satoh, 1996). For example, cytokinin, abscisic acid, and other growth-related compounds that are synthesized in root tissues are involved in stomatal responses (Else et al, 1995;Liang et al, 1997), leaf senescence (Nooden et al, 1990;Soejima et al, 1992), lateral bud development (Bangerth, 1994; Beveridge et al, 1997), flower bud formation (Kinet et al, 1993), leaf greening , and adventitious root formation (Kuroha et al, 2002).Recently, macromolecules have been found in xylem sap, including oligo-and polysaccharides (Satoh et al, 1992; Campbell et al, 1995) and proteins such as peroxidase (Biles and Abeles, 1991), chitinase (Masuda et al, 2001), a cucumber (Cucumis sativus) rootspecific Gly-rich protein (CRGRP; Sakuta et al, 1998;Sakuta and Satoh, 2000), pathogenesis-related (PR) proteins (Rep et al, 2002), a Cys-rich protein (Rep et al, 2003), and a novel 30-kD protein (XSP30; Masuda et al, 1999). However, the regulation of the production of these xylem sap proteins and their physiological functions are not well understood.…”

“…Recently, macromolecules have been found in xylem sap, including oligo-and polysaccharides (Satoh et al, 1992; Campbell et al, 1995) and proteins such as peroxidase (Biles and Abeles, 1991), chitinase (Masuda et al, 2001), a cucumber (Cucumis sativus) rootspecific Gly-rich protein (CRGRP; Sakuta et al, 1998;Sakuta and Satoh, 2000), pathogenesis-related (PR) proteins (Rep et al, 2002), a Cys-rich protein (Rep et al, 2003), and a novel 30-kD protein (XSP30; Masuda et al, 1999). However, the regulation of the production of these xylem sap proteins and their physiological functions are not well understood.…”

“…In our previous study of cucumber xylem sap, a novel 30-kD protein (XSP30) was identified (Masuda et al, 1999). The sequence of the protein encoded by the XSP30 cDNA has significant homology to the B chain of ricin, a toxic protein with Gal-specific lectin activity from the seeds of castor bean (Ricinus communis; Lord et al, 1994).…”