Abstract
BnaC4.BOR1;1c is required for B acquisition in Brassica napus (B. napus) under low B stress. This study aimed to reveal the B regulatory mechanism of BnaC4.BOR1;1c and its physiological roles in B translocation from roots to shoots and B distribution in shoots. Transgenic Arabidopsis plants expressing GUS (β-glucuronidase) under different promoters were generated and the mRNA, and GUS activity was quantitatively measured. The in-situ PCR and immunohistochemistry in B. napus were performed to investigate BnaC4.BOR1;1c expression pattern and localization. Furthermore, assays of B transport and distribution in wild type B. napus and BnaC4.BOR1;1c RNAi lines were carried out to elucidate its physiological roles. Results showed that BnaC4.BOR1;1c mRNA abundance is negatively correlated with B availability, which was mediated by the 29 nt sequence in the 5′ terminal region of 5’-UTR. Besides, the 5’-UTR simultaneously regulates protein expression level, most probably depending on the translation efficiency. BnaC4.BOR1;1c mainly localizes on the plasma membrane of vascular bundle cells in roots and shoots with a polar localization manner that is probably beneficial to B xylem loading in roots and B unloading from xylem to phloem in vascular bundle of shoots. Short-term 10B uptake analysis demonstrates that BnaC4.BOR1;1c preferentially distributes B to developing leaves and flowers under B deficiency. This study reveals combined regulatory action of mRNA abundance and translation efficiency mediated by the 5’-UTR in BnaC4.BOR1;1c in response to B availability and its physiological role in preferential B acquisition in developing tissues of B. napus.
Highlights
Boron (B) is one of the essential micronutrients for plant growth, but B excess is toxic
Results showed that BnaC4.BOR1;1c mRNA abundance is negatively correlated with B availability, which was mediated by the 29 nt sequence in the 5’ terminal region of 5’-UTR
BnaC4.BOR1;1c mainly localizes on the plasma membrane of vascular bundle cells in roots and shoots with a polar localization manner that is probably beneficial to B xylem loading in roots and B unloading from xylem to phloem in vascular bundle of shoots
Summary
Boron (B) is one of the essential micronutrients for plant growth, but B excess is toxic. B is relatively immobile in plant cells; B deficiency defects are early occurred in the developing tissues, such as necrosis and elongation cessation of the root tip, curl and reduced expansion of young leaves, and low fertility (Broadley et al, 2012; Zhang et al, 2017). AtBOR1 functions as a boric acid/borate exporter on the PM of root epidermis and endodermis expression in the cotyledon tip reported (Takano et al, 2002; Yoshinari et al, 2016).
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