The Arabidopsis thaliana ACT4/ACT12 actin gene subclass is strongly expressed throughout pollen development

Abstract

Plants contain complex actin gene families composed of several diverse and ancient subclasses of genes. One Arabidopsis actin gene subclass represented by the ACT4 and ACT12 genes has been isolated and characterized. Both actin genes have typical plant actin gene structures, including three small introns interrupting the coding region and an intron within the mRNA leader. Their encoded proteins differ from each other in only one amino acid, whereas they differ in 3-10% of their amino acids from the other five Arabidopsis actin subclasses. They also share a few small blocks of DNA sequence homology in the 5' flanking region near their TATA boxs, but not in their introns, 3' flanking regions, or degenerate positions within codons. Southern analysis with gene-specific probes from 5' flanking sequences showed that both were single copy genes in the genome. Both RNA gel blot analysis with 3' gene-specific probes and reverse transcriptase-mediated polymerase chain reactions (RT-PCR) with gene-specific primers detected low levels of ACT4 and ACT12 mRNAs in flowers and very high levels in pollen. The RT-PCR detected very low levels of these mRNAs in the vegetative organs. The 5' region from both genes, including the promoter region, TATA box, the sequence for the mRNA leader and its intron, and the first 19 actin codons, was fused to a beta-glucuronidase (GUS) reporter gene. Expression of the GUS fusions were examined histochemically in 40 independent transgenic Arabidopsis plants. Expression of the ACT4/GUS fusion was restricted to young vascular tissues, tapetum, and developing and mature pollen. Similar expression patterns in these tissues and cell types were observed for ACT12/GUS fusion, yet unlike ACT4, ACT12 was also strongly expressed in the root cap and in a ring of pericycle tissues during lateral root initiation and early development. The unique expression patterns of the ACT4/ACT12 actin gene subclass are discussed in light of recent data on the other expressed members of the Arabidopsis actin gene family.

Distribution of actin gene isoforms in the Arabidopsis leaf measured in microsamples from intact individual cells

“…Expression of ACT1, 3, 4, and 12 was never detected in either epidermal or mesophyll samples. These isoforms have been previously reported to be present mainly in reproductive organs Huang et al 1996). We did detect these transcripts in excised leaf samples, presumably from the vascular tissue.…”

“…ACT11 (Huang et al 1997) ACT11 ACT7 ) ACT7 ACT1, ACT3 ) ACT1, ACT3 ACT4, ACT12 (Huang et al 1996) ACT4, ACT12…”

“…The actin gene isoforms are particularly well suited for such a study, as the Arabidopsis genome potentially encodes 10 isoforms, of which 8 are expressed at detectable levels McKinney and Meagher 1998). Information on the distribution of the isoforms is already available following RT-PCR analysis of excised tissues and in vivo expression of a b-glucuronidase (GUS) reporter gene linked to specific actin promoters Huang et al 1996Huang et al , 1997McDowell et al 1996a). Recently, Kandasamy et al (1999) used class-specific antibodies to visualize the distribution of the protein.…”

Identification and molecular characterization of novel anther-specific genes in Oryza sativa L. by using cDNA microarray

“…These duplicated clones, which were scattered on the microarray glass slide showed quite similar expression profiles. The other point was that several clones identical to the genes, which had been already characterized as anther-and/or pollen-specific, were identified in several clusters (Tsuchiya et al 1992;Tsuchiya et al 1994;Hihara et al 1996;Wang et al 2003;Li et al 2003;Kim et al 1993;Huang et al 1996;Albani et al 1992;Niogret et al 1991; Table 3). …”

Dissection of Arp2/3 Complex Actin Nucleation Mechanism and Distinct Roles for Its Nucleation-Promoting Factors in Saccharomyces cerevisiae

“…The Arp2/3 complex is composed of seven subunits: Arp3, Arp2, p40/ ARPC1, p35/ARPC2, p21/ARPC3, p19/ARPC4, and p15/ARPC5 (Machesky et al 1994). Arp2 and Arp3 are 46 and 39% identical to actin, respectively (LeesMiller et al 1992;Schwob and Martin 1992;Huang et al 1996), and are predicted to directly nucleate actin polymerization. This is predicted on the basis of high degree of sequence and structural homology among Arp2, Arp3, and conventional actin, particularly at the barbed end of these proteins, i.e., subdomains I and III (Kelleher et al 1995;Robinson et al 2001).…”