Abstract
In the agriculture industry, adventitious root formation is a core issue of plants asexual propagation. However, the underlying molecular mechanism of adventitious root formation is far beyond understanding. In present study we found that target of rapamycin (TOR) signaling plays a key role in adventitious root formation in potato and Arabidopsis. The core components of TOR complex including TOR, RAPTOR, and LST8 are highly conserved in potato, but the seedlings of potato are insensitive to rapamycin, implying FK506 Binding Protein 12 KD (FKBP12) lost the function to bridge the interaction of rapamycin and TOR in potato. To dissect TOR signaling in potato, the rapamycin hypersensitive potato plants (BP12-OE) were engineered by introducing yeast FKBP12 (ScFKBP12) into potato. We found that rapamycin can significantly attenuate the capability of adventitious root formation in BP12-OE potatoes. KU63794 (KU, an active-site TOR inhibitor) combined with rapamycin can more significantly suppress adventitious root formation of BP12-OE potato than the single treatments, such as KU63794 or rapamycin, indicating its synergistic inhibitory effects on potato adventitious root formation. Furthermore, RNA-seq data showed that many genes associated with auxin signaling pathway were altered when BP12-OE potato seedlings were treated with rapamycin + KU, suggesting that TOR may play a major role in adventitious root formation via auxin signaling. The auxin receptor mutant tir1 was sensitive to TOR inhibitors and the double and quadruple mutants including tir1afb2, tir1afb3, and tir1afb1afb2afb3 displayed more sensitive to asTORis than single mutant tir1. Consistently, overexpression of AtTIR1 in Arabidopsis and potato can partially overcome the inhibitory effect of asTORis and promote adventitious root formation under asTORis treatments. These observations suggest that TOR signaling regulates adventitious root formation by mediating auxin signaling in Arabidopsis and potato.
Highlights
During the growth and development of plants, root systems play fundamental roles in absorbing water and mineral nutrition, anchoring plant, and synthesis of various growth factors such as hormone to regulate plant growth and development(Torrey and Phillips, 1974; Russell, 1977; Ljung et al, 2005)
Choi et al (1996) reported that rapamycin can interact with the FRB domain of target of rapamycin (TOR) through close contacting with aromatic residues, such as Tyr1934, Phe1935, Trp2001, Tyr2005, Phe2008, Ser1931, Leu1927, Thr1998, and Asp2002. We found these key AA residues were highly conserved between potato, Arabidopsis and human through aligning the amino acid sequence of FRB domain of TOR from different species (Figure S1A), indicating that the function of TOR in potato could be dissected by using the rapamycin-FK506 Binding Protein 12 KD (FKBP12)-TOR negative regulation system
The plant TOR research could trace back to 1998, when Xu et al reported the V. faba FKBP12 could not mediate the action of FK506 and rapamycin to combine with TOR (Xu et al, 1998)
Summary
During the growth and development of plants, root systems play fundamental roles in absorbing water and mineral nutrition, anchoring plant, and synthesis of various growth factors such as hormone to regulate plant growth and development(Torrey and Phillips, 1974; Russell, 1977; Ljung et al, 2005). Adventitious root formation has become a core issue both on the theoretical aspect of plant development, organogenesis and on the practical side of plant asexual propagation (Thorpe et al, 1991; Klerk et al, 1999; Abarca and Díazsala, 2009; Li et al, 2009; Amissah et al, 2013; Bellini et al, 2014; Liu et al, 2014; Verstraeten et al, 2014; Hu and Xu, 2016). The available whole-genome sequence and efficient and reliable transformation systems of potato allow it to become an important research model for adventitious root formation
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