Pex1, a pollen-specific gene with an extensin-like domain.

Abstract

We report here the identification of a pollenspecific gene from Zea mays that contains multiple Ser-(Pro).repeats, the motif found in the cell wall-associated extensins.Sequence analysis reveals that the encoded protein has a putative globular domain at the N terminus and an extensinlike domain at the C terminus. (3)(4)(5)(6). In addition, stylar tissues are known to secrete AGPs (7). It is known that pollen is enriched for hydroxyproline (8-11). Therefore, it seems likely that pollen also contains HRGPs. These extracellular proteins may play a structural role in the extremely rapid cell elongation that occurs during pollen tube growth (12). Alternatively, pollen HRGPs are potential candidates for mediating pollen-pistil interactions in conjunction with partner molecules in female tissues. We have isolated a pollen-specific gene that appears to be a member of a small gene family in maize and encodes multiple repeats of the extensin-like motif Ser-(Pro)4. Pexl (pollen extensin-like) differs from other maize HRGP genes in that it contains significant numbers of this canonical extensin repeat motif. Isolation of a genomic clone representing the Pexi gene revealed a protein structure containing both an extensin-like domain and a putative globular domain.J MATERIALS AND METHODS Maize inbred lines Ky2l and B73 were grown under standard greenhouse conditions. Microspores and immature pollen were staged by the method of Bedinger and Edgerton (13). Mature pollen was collected from shedding tassels. Young leaves were wounded by clamping with a hemostat and were collected 6 and 24 hr after wounding.The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. pSF66 and pSF21 were isolated from a cDNA library prepared from poly(A)+ RNA from immature starch-filled pollen (maize inbred line Ky2l) and cloned into AZAP (Stratagene) with EcoRI-Not I adapters (Invitrogen). Recombinant phage were differentially screened with cDNA probes made by using mRNA from immature starch-filled pollen and from endosperm. Plaques that hybridized uniquely with immature pollen mRNA were selected and rescreened.A genomic library prepared from Sau3A1 partial digests of maize inbred line B73 DNA cloned into phage AEMBL3 arms was purchased from Clontech. In all, 240,000 plaques, representing half a genome of DNA, were screened with pSF21 cDNA as a probe. Two positive clones were identified. One of these was subcloned into pBluescript (Stratagene).A 7.3-kb BamHI subclone containing sequences hybridizing to pSF21 was designated pZmPl. Four thousand three hundred thirty-one base pairs of pZmPl were sequenced by the dideoxy method (14) using Sequenase (United States Biochemical) and [a-32P]dATP (Amersham). Sequences of pZmPl were confirmed by the University of North Carolina, Chapel Hill, Automated DNA Sequencing Facility on a model 373A DNA sequencer using the Taq DyeDeoxy terminator cycle sequenci...

Whole-Genome Comparison of Leucine-Rich Repeat Extensins in Arabidopsis and Rice. A Conserved Family of Cell Wall Proteins Form a Vegetative and a Reproductive Clade,

“…The LRX1 protein is specifically targeted to the root hair cell wall, where it is insolubilized. Similarly, PEX1, a pollen-specific maize (Zea mays) LRX, was immunolocalized in the intine layer of the pollen grain and the callosic sheath of the pollen tube (Rubinstein et al, 1995a(Rubinstein et al, , 1995b. Together, the properties of LRR and extensins, the cell wall localization of LRX proteins, and the phenotype of lrx1 mutants suggest that LRXs are potentially involved in the regulation of cell wall expansion in response to signaling.…”

“…The specific members of the "reproductive clade (see below) are referred to as PEX genes with a similar modifier (i.e. Pex1 [Rubinstein et al, 1995a] is now ZmPEX1). We believe that this system minimizes confusion, while still maintaining the links to the previous published work.…”

“…The prediction of the AtLRX open reading frames (ORFs) was verified by visually checking the threeframe translations of the genomic sequences and by comparing the predicted proteins with the AtLRX1, ZmPEX1, and ZmPEX2 sequences (Rubinstein et al, 1995a;Baumberger et al, 2001;Stratford et al, 2001). The OsLRX ORFs were determined similarly, after correction of the ambiguities and sequencing errors by comparison with ESTs and rice subsp.…”

“…The LRX genes are dispersed on the five Arabidopsis chromosomes and on seven rice chromosomes. The nomenclature used to identify the individual genes has been developed based on previous work (Rubinstein et al, 1995a(Rubinstein et al, , 1995bBaumberger et al, 2001; this study). The gene family is referred to as the LRX gene family.…”

“…Recently, a new type of modular cell wall protein containing a Leu-rich repeat (LRR) and an extensin domain was described in eudicots and monocots (Rubinstein et al, 1995a;Baumberger et al, 2001;Stratford et al, 2001). LRRs are frequently implicated in protein-protein interactions and, in plants, a large subclass of receptor-like kinases has extracellular LRRs in the receptor domain (Shiu and Bleecker, 2001).…”