The KNAT1 gene is a member of the Class I KNOXhomeobox gene family and is thought to play an important role in meristem development and leaf morphogenesis. Recent studies have demonstrated that KNAT1/BP regulates the architecture of the inflorescence by affecting pedicle development in Arabidopsis thaliana. Herein, we report the characterization of an Arabidopsis T-DNA insertion mutant that shares considerable phenotypic similarity to the previously identified mutant brevipedicle （bp）. Molecular and genetic analyses showed that the mutant is allelic to bp and that the T-DNA is located within the first helix of the KNAT1 homeodomain （HD）. Although the mutation causes a typical abnormality of short pedicles, propendent siliques, and semidwarfism, no obvious defects are observed in the vegetative stage. A study on cell morphology showed that asymmetrical division and inhibition of cell elongation contribute to the downward-pointing and shorter pedicle phenotype. Loss of KNAT/BPfunction results in the abnormal development of abscission zones. Mlcroarray analysis of gene expression profiling suggests that KNAT1/BP may regulate abscission zone development through hormone signaling and hormone metabolism in Arabidopsis.
Xiao-Qun WangWei-Hui XuLi-Geng MaZhi-Ming FuXing-Wang DengJia-Yang LiYong-Hong Wang
Tiller angle of rice （Oryza sativa L.） is an important agronomic trait that contributes to grain production, and has long attracted attentions of breeders for achieving ideal plant architecture to improve grain yield. Although enormous efforts have been made over the past decades to study mutants with extremely spreading or compact tillers, the molecular mechanism underlying the control of tiller angle of cereal crops remains unknown. Here we report the cloning of the LAZY1 （LA1） gene that regulates shoot gravitropism by which the rice tiller angle is controlled. We show that LA1, a novel grass-specific gene, is temporally and spatially expressed, and plays a negative role in polar auxin transport （PAT）. Loss-of-function of LA1 enhances PAT greatly and thus alters the endogenous IAA distribution in shoots, leading to the reduced gravitropism, and therefore the tiller-spreading phenotype of rice plants.
Peijin LiYonghong WangQian QianZhiming FuMei WangDali ZengBaohua LiXiujie WangJiayang Li
Brassinosteroids （BRs） are a major group of plant hormones that regulate plant growth and development. BRI1, a protein localized to the plasma membrane, functions as a BR receptor and it has been proposed that its kinase activity has an essential role in BR-regulated plant growth and development. Here we report the isolation and molecular characterization of a new allele of bril, bril-301, which shows moderate morphological phenotypes and a reduced response to BRs under normal growth conditions. Sequence analysis identified a two-base alteration from GG to AT, resulting in a conversion of 989G to 9891 in the BRI1 kinase domain. An in vitro assay of kinase activity showed that bril-301 has no detectable autophosphorylation activity or phosphorylation activity towards the BRI1 substrates TTL and BAK1. Furthermore, our results suggest that bril-301, even with extremely impaired kinase activity, still retains partial function in regulating plant growth and development, which raises the question of whether BRI1 kinase activity is essential for BR-mediated growth and development in higher plants.
Weihui XuJuan HuangBaohua LiJiayang LiYonghong Wang
The plant tryptophan （Trp） biosynthetic pathway produces many secondary metabolites with diverse functions. Indole- 3-acetic acid （IAA）, proposed as a derivative from Trp or its precursors, plays an essential role in plant growth and development. Although the Trp-dependant and Trp-independent IAA biosynthetic pathways have been proposed, the enzymes, reactions and regulatory mechanisms are largely unknown. In Arabidopsis, indole-3-glycerol phosphate （IGP） is suggested to serve as a branchpoint component in the Trp-independent IAA biosynthesis. To address whether other enzymes in addition to Trp synthase ~ （TSA1） catalyze IGP cleavage, we identified and characterized an indole synthase （INS） gene, a homolog of TSA1 in Arabidopsis. INS exhibits different subcellular localization from TSA1 owing to the lack of chloroplast transit pepUde （cTP）. In si//co data show that the expression levels of INS and TSA1 in all examined organs are quite different. Histochemical staining of INS promoter-GUS transgenic lines indicates that INS is expressed in vascular tissue of cotyledons, hypocotyls, roots and rosette leaves as well as in flowers and siliques. INS is capable of complementing the Trp auxotrophy of Escherichia co// AtrpA strain, which is defective in Trp synthesis due to the deletion of TSA. This implies that INS catalyzes the conversion of IGP to indole and may be involved in the biosynthesis of Trp-independent IAA or other secondary metabolites in Arabidopsis.
The KNAT1 gene is a member of the Class I KNOX homeobox gene family and is thought to play an important role i...
Xiao-Qun Wang,Wei-Hui Xu,Li-Geng Ma,Zhi-Ming Fu,Xing-Wang Deng,Jia-Yang Li and Yong-Hong Wang State Key Laboratory of Plant Genomics and National Center for Plant Gene Research,Institute of Genetics and Developmental Biology,the Chinese Academy of Sciences,Beijing 100101,China Peking-Yale Joint Center of Plant Molecular Genetics and Agrobiotechnology,College of Life Sciences,Peking University,Beijing 100871,China National Institute of Biological Sciences,Zhongguancun Biological Science Park,Beijing 102206,China
