Tribenuron-Methyl Induces Male Sterility through Anther-Specific Inhibition of Acetolactate Synthase Leading to Autophagic Cell Death

Abstract

Tribenuron-methyl (TM) is a powerful sulfonylurea herbicide that inhibits branched-chain amino acid (BCAA) biosynthesis by targeting the catalytic subunit (CSR1) of acetolactate synthase (ALS). Selective induction of male sterility by foliar spraying of TM at low doses has been widely used for hybrid seed production in rapeseed (Brassica napus); however, the underlying mechanism remains unknown. Here, we report greater TM accumulation and subsequent stronger ALS inhibition and BCAA starvation in anthers than in leaves and stems after TM application. Constitutive or anther-specific expression of csr1-1D (a CSR1 mutant) eliminated anther-selective ALS inhibition and reversed the TM-induced male sterile phenotype in both rapeseed and Arabidopsis. The results of TM daub-stem experiments, combined with the observations of little TM accumulation in anthers and reversion of TM-induced male sterility by targeted expression of the TM metabolism gene Bel in either the mesophyll or phloem, suggested that foliar-sprayed TM was polar-transported to anthers mainly through the mesophyll and phloem. Microscopy and immunoblotting revealed that autophagy, a bulk degradation process induced during cell death, was elevated in TM-induced male sterile anthers and by anther-specific knockdown of ALS. Moreover, TM-induced pollen abortion was significantly inhibited by the autophagy inhibitor 3-MA. These data suggested that TM was polar-transported to anthers, resulting in BCAA starvation via anther-specific ALS inhibition and, ultimately, autophagic cell death in anthers.

Exposure to trace amounts of sulfonylurea herbicide tribenuron-methyl causes male sterility in 17 species or subspecies of cruciferous plants

“…Thus, an application of ALS-inhibiting gametocides on model plant A. thaliana to replace manual emasculation will be of interest to geneticists when they wish to make many genetic crosses. The results of the present study, combined with previous studies [12–14, 23, 24], suggest the possible use of other sulfonylurea chemicals as gametocides for cruciferous plants. The alternate use of other gametocides can resolve the concerns of insensitivity to tribenuron-methyl in some special genotypes.…”

“…A high level of MS induced by tribenuron-methyl brings an opportunity for the utilization of heterosis of these minor crops that belong to Brassicaceae including S. alba, E. sativa, C. sativa, C. bursa-pastoris, and M. incana . A previous study also reported that a foliar spray of 15 ng of tribenuron-methyl per plant of A. thaliana had a gametocidal effect [23]. In addition, exposure to trace concentrations of imazethapyr, an ALS-inhibitor, had unstable gametocidal effects on Brassica plants [13] and affected floral organ development and reproduction in A. thaliana [24].…”

“…Thus, the proper dose to every treated plants needs to be carefully calibrated and distributed by a precise spray. A substitution for spraying is to smear or daub the gametocide on the stem of the plant [23] with a soft adhesive substance additive such as lanolin cream. Moreover, frequent rainfall at the bolting stage limits the application of a gametocide.…”

Suppressor of rid1 (SID1) shares common targets with RID1 on florigen genes to initiate floral transition in rice

“…Full-length cDNA of SID1 were amplified with primer pair SID1(CDs)-OX-F/SID1(CDs)-OX-R and then cloned into pU2301 by Kpn I- BamH I digestion; full-length cDNA of RID1 was amplified with primer pair RID1(cDNA)-OX-F/RID1(cDNA)-OX-R and then cloned into pU2301 by Kpn I- BamH I digestion. To investigate the tissue-specific expression of SID1 , approximately 3-kb promoter fragments of SID1 were amplified from genomic DNA and then cloned into pC2300-EX-GUS [53] to create pSID1 :: GUS . To introduce targeted mutations in SID1 protein, sgRNA:Cas9 expression vector of the SID1 gene was constructed as described previously [44].…”

Partial Male Sterility in Imisun Sunflower: Imazapyr Treatment in Advanced Vegetative Stages Decreases Pollen Yield and Alters ahas Gene Expression

“…Zhao et al (2015) proposed that BCAA starvation induces pollen formation failure and ultimately leads to autophagic cell death in the anthers. The AHAS-inhibitory hybridization agent used in rapeseed (Brassica napus L.) is tibenuron methyl.…”