Abstract
Auxin is an important phytohormone that regulates response, differentiation, and development of plant cell, tissue, and organs. Along with its local production, long-distance transport coordinated by the efflux/influx membrane transporters is instrumental in plant development and architecture. In the present study, we cloned and characterized a wheat (Triticum aestivum) auxin efflux carrier ABCB1. The TaABCB1 was physically localized to the proximal 15% of the short arm of wheat homoeologous group 7 chromosomes. Size of the Chinese spring (CS) homoeologs genomic copies ranged from 5.3–6.2 kb with the 7A copy being the largest due to novel insertions in its third intron. The three homoeologous copies share 95–97% sequence similarity at the nucleotide, 98–99% amino acid, and overall Q-score of 0.98 at 3-D structure level. Though detected in all analyzed tissues, TaABCB1 predominantly expressed in the meristematic tissues likely due to the presence of meristem-specific activation regulatory element identified in the promoter region. RNAi plants of TaABCB1 gene resulted in reduced plant height and increased seed width. Promoter analysis revealed several responsive elements detected in the promoter region including that for different hormones as auxin, gibberellic acid, jasmonic acid and abscisic acid, light, and circadian regulated elements.
Highlights
The role of auxin as a growth regulator was perceived long before it was isolated from plant tissue[1,2,3]
Sequence coverage was 85% between 7A and 7B, and 7A and 7D, and 99.6% between 7B and 7D while nucleotide sequence identity ranged from 95.41–98.76% among the three homoeologous copies both at genomic as well as cDNA level (Table 2)
The ABCB1 is involved in long-distance auxin transport influencing morpho-physiological responses
Summary
The role of auxin as a growth regulator was perceived long before it was isolated from plant tissue[1,2,3]. Along with its local production, the auxin synthesized in the shoot apical meristem (SAM), leaf primordia, young leaves, and other actively dividing cells is transported through directional flow via vascular and bundle sheath cells, generating a concentration gradient. This directional flow or polar auxin transport (PAT) is mediated via auxin influx/efflux trans-membrane proteins including AUX1/LIKE AUX1 (AUX1/LAX), PIN-FORMED (PIN) and ATP-binding cassette subfamily B (ABCB)(for details see review[4,5]). We cloned and characterized the TaABCB1, analyzed its predicted promoter sequences, studied its spatial and temporal expression pattern, and showed its role in influencing agronomic characteristics in bread wheat
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