tassel-less1 Encodes a Boron Channel Protein Required for Inflorescence Development in Maize

Abstract

tassel-less1 (tls1) is a classical maize (Zea mays) inflorescence mutant. Homozygous mutant plants have no tassels or very small tassels, and ear development is also impaired. Using a positional cloning approach, ZmNIP3;1 (a NOD26-like intrinsic protein) was identified as the candidate gene for tls1. The ZmNIP3;1 gene is completely deleted in the tls1 mutant genome. Two Mutator-insertional TUSC alleles of ZmNIP3;1 exhibited tls1-like phenotypes, and allelism tests confirmed that the tls1 gene encodes ZmNIP3;1. Transgenic plants with an RNA interference (RNAi) construct to down-regulate ZmNIP3;1 also showed tls1-like phenotypes, further demonstrating that TLS1 is ZmNIP3;1. Sequence analysis suggests that ZmNIP3;1 is a boron channel protein. Foliar application of boron could rescue the tls1 phenotypes and restore the normal tassel and ear development. Gene expression analysis indicated that in comparison with that of the wild type or tls1 plants treated with boron, the transition from the vegetative to reproductive phase or the development of the floral meristem is impaired in the shoot apical meristem of the tls1 mutant plants. It is concluded that the tls1 mutant phenotypes are caused by impaired boron transport, and boron is essential for inflorescence development in maize.

Transport of Boron by thetassel-less1Aquaporin Is Critical for Vegetative and Reproductive Development in Maize

“…An additional allele identified from the RescueMu population had a Mu insertion in the 59 untranslated region ( Figure 5B). Attempts to amplify any part of the tls1 coding region (AGPv2 (Leonard et al, 2014). In summary, the identification of eight tls1 alleles with mutations in the maize NIP3;1 confirms that tls1 encodes the major intrinsic protein NIP3;1.…”

“…Bayesian phylogenetic analysis of maize tls1 and similar NIPs from other plant species revealed that tls1 falls in a well-supported (>0.95 posterior probability) monocot-specific clade along with rice NIP3;1a ( Figure 6) (Hanaoka et al, 2014;Leonard et al, 2014). This grass tls1 clade is sister to another well-supported grass clade containing four rice sequences, three sorghum (Sorghum bicolor) sequences, and the maize NIP471 sequence.…”

“…Six mutants with either a reduced or completely absent tassel and the same suite of phenotypes as the original tls1-reference (tls1-ref) allele were identified (Albertsen et al, 1993;Leonard et al, 2014) (M. Albertsen, personal communication). The tls1-ref allele had been introgressed into B73 and hence was used for further analyses (unless otherwise stated) and is hereafter referred to as tls1.…”

“…Alignment of the TLS1 protein sequence to orthologs from other plant species showed that TLS1 shares 74 and 63% identity with Arabidopsis NIP5;1 and NIP6;1, respectively, and 90% identity with rice NIP3;1a (Supplemental Figure 5) (Hanaoka et al, 2014;Leonard et al, 2014). TLS1, At-NIP5;1 and Os-NIP3;1a are conserved at the dual NPA and ar/R motifs ( Figure 5C; Supplemental Figure 5; NPS/NPV and AIGR, respectively), which regulate substrate specificity, suggesting that all three proteins may function in the transport of similar molecules.…”

Preferential Distribution of Boron to Developing Tissues Is Mediated by the Intrinsic Protein OsNIP3

“…In Arabidopsis, NIP5;1 and BOR1 are polarly localized at the distal and proximal side of the plasma membrane of the root cells, respectively (Takano et al, 2010), and their cooperative transport is required for efficient and directional uptake of B in the roots especially under a B-limited condition Reid 2014). Homologs of Arabidopsis NIP5;1 and BOR1 have been functionally characterized in other plant species such as rice (Oryza sativa), barley (Hordeum vulgare), rapeseed (Brassica napus), and maize (Zea mays; Nakagawa et al, 2007;Sutton et al, 2007;Chatterjee et al, 2014;Durbak et al, 2014;Hanaoka et al, 2014;Leonard et al, 2014;Zhang et al, 2017). Basically, they have a similar role in B uptake, although the expression patterns differ somewhat within plant species.…”