An early auxin-responsive Aux/IAA gene from wheat (Triticum aestivum) is induced by epibrassinolide and differentially regulated by light and calcium

Abstract

The plant hormone auxin plays a central role in regulating many aspects of plant growth and development. This largely occurs as a consequence of changes in gene expression. The Aux/IAA genes are best characterized among the early auxin-responsive genes, which encode short-lived transcriptional repressors. In most plants examined, including Arabidopsis, soybean, and rice, the Aux/IAA genes constitute a large gene family. By screening the available databases, at least 15 expressed sequence tags (ESTs) have been identified from wheat (Triticum aestivum), which exhibit high sequence identity with Aux/IAA homologues in other species. One of these Aux/IAA genes, TaIAA1, harbouring all the four conserved domains characteristic of the Aux/IAA proteins, has been characterized in detail. The expression of TaIAA1 is light-sensitive, tissue-specific, and is induced within 15-30 min of exogenous auxin application. Also, the TaIAA1 transcript levels increase in the presence of a divalent cation, Ca(2+), and this effect is reversed by the calcium-chelating agent, EGTA. The TaIAA1 gene qualifies as the primary response gene because an increase in its transcript levels by auxin is unaffected by cycloheximide. In addition to auxin, the TaIAA1 gene is also induced by brassinosteroid, providing evidence that interplay between hormones is crucial for the regulation of plant growth and development.

Teaching an Old Hormone New Tricks: Cytosolic Ca2+ Elevation Involvement in Plant Brassinosteroid Signal Transduction Cascades

“…In a manner similar to that already demonstrated for orthologous genes in rice (Oryza sativa; Song et al, 2009) and wheat (Singla et al, 2006), we found that BR application to Arabidopsis seedlings increased the expression of IAA1 in Ws-2 wildtype plants (Fig. 6).…”

“…( Fig. 7), a gene known to be responsive to BR (Singla et al, 2006;Song et al, 2009). Further experiments examining IAA1 expression are consistent with this model (Fig.…”

“…DWARF1, an enzyme involved in BR synthesis, is activated by Ca 2+ /calmodulin (CaM); this would suggest that on a long-term basis, the Ca 2+ status of cells might impact the generation or steady-state level of the steroidal hormone (Du and Poovaiah, 2005). A report on hormone signaling in wheat (Triticum aestivum; Singla et al, 2006) Figure 1, we observed an elevation in cytosolic Ca 2+ initiating seconds after adding BR to leaves from ecotype Wassilewskija (Ws-2) wild-type plants. The bri1-5 genotype has reduced sensitivity to BR .…”

Epibrassinolide regulated synthesis of polyamines and auxins in Raphanus sativus L. seedlings under Cu metal stress

“…Vert et al (2008) studied synergistic interactions of BRs and auxins and reported integration of auxins and brassinosteriod pathways by auxins response factors responsible for synergism between BRs and auxins. Elevated expression of TaIAA1 gene of Aux/IAA gene family on application of 24-epiBL in wheat was also recorded (Singla et al, 2006). Similarly, the stress protective role of auxins against heavy metals was also observed by Dimpka et al (2008) in Streptomyces spp.…”

Light control of shoot regeneration in callus cultures derived from barley (Hordeum vulgare L.) immature embryos

“…Kraepiel et al (1995) indicated that the isoforms of light-expressed phytochrome controlled the endogenous indole-3-acetic acid (IAA) level of calli in Nicotiana plumbaginifolia. Results of recent studies suggest the existence of cross-talk between auxin and light signaling (Salisbury et al 2007, Sibout et al 2006, Singla et al 2006. On the other hand, Bangerth (2001a, 2001b) indicated that endogenous hormone levels differed depending on the competence of calli; embryogenic calli showed higher IAA and lower cytokinin than non-embryogenic calli.…”