Untitled

Abstract

In maize, a layer of basal endosperm cells adjacent to the pedicel is modified for a function in solute transfer. Three genes specifically expressed in this region, termed the basal endosperm transfer layer (BETL-2 to -4), were isolated by differential hybridization. BETL-2 to -4 are coordinately expressed in early and mid-term endosperm development, but are absent at later stages. BETL-2 to -4 coding sequences all predict small (< 100 amino acids), secreted, cysteine-rich polypeptides which lack close relatives in current database accessions. BETL-3 and BETL-1 display some sequence similarities with each other and to plant defensins. BETL-2 to -4 promoter regions were isolated and compared, revealing the presence of a promoter-proximal microsatellite repeat as the most highly conserved sequence element in each sequence. Electrophoretic mobility shift assays (EMSA) showed that specific BETL-2 to -4 promoter fragments competed for binding to the same DNA-binding activity in nuclear extracts prepared from maize endosperm. Although BETL-2 to -4 are only expressed in basal endosperm cells, the DNA-binding activities detected were of two types: distal endosperm-specific, or present in both basal and distal endosperm extracts. On the basis of these findings, a model to account for the coordinate regulation of BETL genes in endosperm cells is proposed.

Two maize END-1 orthologs, BETL9 and BETL9like, are transcribed in a non-overlapping spatial pattern on the outer surface of the developing endosperm

“…That being the case, BETL9 would add to the number of proteins expressed at the BETL with presumed or already proven anti pathogenic activity. BETL1 , BETL3, and meg-1 (Hueros et al, 1995, 1999; Gutiérrez-Marcos et al, 2004) genes code for proteins related to the antimicrobial peptides defensins. BETL4 has some similarity to alpha-amylase/trypsin inhibitors (Thompson et al, 2001) and BETL2 was renamed as BAP-2 (basal layer antifungal protein 2) after been demonstrated that it has antifungal activity in vitro (Serna et al, 2001).…”

“…In maize there is already an extensive collection that includes genes named as BETL1 , 2 , 3, and 4 (Hueros et al, 1995, 1999) encoding for small cysteine-rich proteins. The product of the BETL2 gene was renamed BAP-2 (basal layer antifungal protein 2) after its in vitro antifungal activity was demonstrated (Serna et al, 2001).…”

On the track of transfer cell formation by specialized plant-parasitic nematodes

“…Although little is known about the molecular signals that induce TC differentiation, some genes expressed associated with TCs have been described (Hueros et al, 1995, 1999; Gómez et al, 2002; Gutiérrez-Marcos et al, 2004; Muñiz et al, 2006). Among these the Myb-related protein-1 ( MRP-1 ) was the first TC-specific transcriptional activator identified in plants (Gómez et al, 2002) and was shown to be a key regulator of TCs differentiation process in maize endosperm (Gómez et al, 2009).…”

Atypical response regulators expressed in the maize endosperm transfer cells link canonical two component systems and seed biology

“…In particular, sugars and the hormones abscisic acid (ABA) and cytokinin have been shown to reach the mother-seed interface in high concentrations and affect the kernel development significantly [17-19], suggesting that transfer cells possibly play a role in the interpretation and further transmission of those signals. In recent years a number of transfer cell specific genes have been described [20-22] including a MYB-related transcription factor, ZmMRP-1 , which controls the expression of several of these genes [23] through interaction with specific DNA motifs in their promoters [24]. In a previous paper we reported the isolation of ZmTCRR-1 , a type-A response regulator exclusively expressed in the transfer cell layer of the maize caryopsis during early development, and transcriptionally controlled by ZmMRP-1 .…”