生长素作用机制Mechanism of Auxins Action

The developmental processes that are controlled by auxin flux

Control of leaf vein formation by polar auxin transport.

Queations1.Discuss the evidence for the role of auxin in the following physiological phenomena: apical dominance, lateral and adventitious roots, leaf abscission, floral bud development, fruit development, and vascular differentiation.

2. What is ABP1? Which auxin responses does it seem to regulate?

3. What are early auxin-responsive genes?

4. Diagram and discuss the current model for the role of the AUX/IAA gene family in regulating the early auxin-responsive genes.

ABP1 and downstream auxin responses

ABP1 is located both in the ER and at the outer face of the plasma membrane but the ABP1 in ER does not bind auxin.

ABP1 located at the plasma membrane is involved in the control of early auxin electrophysiological responses.

控制生长素的转录反应 Aux/IAA 家族属于生长素快速诱导的半衰期很短

的核蛋白，有 4 个保守结构域 . 其中结构域Ⅱ的13 个氨基酸特异序列是 Aux / IAA 蛋白家族中共有的保守序列。

ARF 生长素响应因子能与生长素早期反应基因启动子中的生长素应答元件（ AuxRE ） TGTCTC 序列特异性结合，由氨基酸的组成决定该蛋白具有调节生长素反应基因表达的转录激活或抑制作用 .

(A) ARF protein binds an AuxRE promoter

element.

Under low-auxin conditions, Aux/IAA

repressor binds ARF via

heterodimerization between Aux/IAA and

ARF domains III and IV.

(B) Auxin promotes Aux/IAA domain II-TIR1

association, bringing the Aux/IAA protein

to the SCFTIR1 complex for ubiquitination

and subsequent destruction by the 26S

proteasome.

The activating ARF, with a Gln-rich (Q)

middle domain, is then freed to promote

auxin-induced gene expression.

Woodward and Bartel, 2005

By interacting with specific substrates, the F-box proteins

confer specificity to the degradation machinery.

Chaperone Mediated Protein Folding & Misfolding

Degradation of Misfolded Proteins

Lysosomal (extracellular) protein degradationProtein degraded by lysosomal enzymes

Cytosolic (intracellular) protein degradationThe Ubiquitin Proteosome pathway

Cytosolic protein degradation

The Ubiquitin Proteosome Pathway

www.ihf.de/forschung/ popup/ubiquitin.html

TIR1, a F-box protein, is an auxin receptor

Insensitive responses

WT

tir1

Kepinski and Leyser, 2005

Interact with Aux/IAA domain II peptides in an auxin-dependent

manner.

Rapid association and dissociation of

TIR1–Aux/IAA complexes.

• ATPase is rapidly

stimulated by auxin

,ABP1 is the

receptor relevant

for this process.

• Auxin induced de-

novo synthesis of

ATPase.

Crosslink of ABP1 and TIR1 signaling pathways

Christian et al., 2006

Many of the proteins involved in plant hormone signalling pathways have been identified.

Strikingly, the ubiquitin–proteasome pathway plays a central part in most hormone-signalling pathways.

Hormone signalling is integrated at several levels during plant growth and development.

The Ubiquitin-Proteasome Pathway and Plant Development

The Plant Cell, 2004,16, 3181–3195

The ubiquitin/26S proteasome (Ub/26S) pathway in Arabidopsis thaliana .

The family of E3 ubiquitin ligases

Single subunit ring E3s

Multisubunit ring E3s ＳＣＦCUL3-BTB

APC

COP1

SINAT5

ARC1

SCF 复合体主要由 4 种蛋白组成：Skp1 ， Cullin （酵母中是 Cdc53 ）， Roc1 / Rbx1 / Hrt1 及 F-box 蛋白 .

UbE1

ATP AMP

E2

E2

E1

E2E3substrate

S

E1 SH

SH

SH

S

S

E3

substrate

26S proteasome

The Ubiquitination-Proteasome Pathway

Plant Sumoylation System

Model of auxin action

SCFTIR1-Aux / IAA 复合体

A direct auxin-dependent interaction between the F-box protein TIR1 and several AUX/IAA proteins has been demonstrated, and two AUX/IAA proteins (IAA7 and IAA17) are stabilized in the tir1 mutant.

(Nature Chemical Biology,2009,5:301-307)

黄少明介绍

Auxin response factor 2 (ARF2) plays a major role in regulating auxin-mediated leaf longevity

Model depicting interactions between auxin function components and key genetic pathways controlling leaf development in Arabidopsis thaliana

Domain structures of the Aux/IAA and ARF families found in A. thaliana, S. moellendorffii and P. patens.

BMC Evolutionary Biology 2009, 9:126

HECT

RING/U-Box

SCF F-box

APC Apc10

E2

E1

E3

S. cerevisiae A. thalianaH. sapiens

Number in gene family

1 2 2

45

7

600 20

694

13 50

5 50

48 >500

12 1

14 38

Evolutionary distribution of Ubiquitin processing enzymes

赤霉素作用机制Mechanism of Gibberellins Action

Gibberellins stimulate cell elongation and cell division

Gibberellins enhance cell wall extensibity without acidification

Gibberellins regulate the transcription of cell cycle kinases in intercalary meristem

Gibberellins: Regulators of plant height

Pea as a Model System to Study Hormonal Interaction

Seeds Required for Pericarp Growth and Bioactive GA1 Production

GA Signaling Intermediates GAI (a protein coded by GA-Insensitive

gene ) RGA ( a negative factor) SPY ( a negative regulator of GA responses)

SPY 序列与动物的氧 - 乙酰 - 葡糖胺转移酶（ O-GlaNAC transferase, OGT ）高度相似 . 将 UDP-GlcNAc 的 GlcNAc 转移到目标蛋白 Ser/Thr 残基上 ,促进 RGA 和 GAI 阻碍 GA 诱导基因的表达 .

GRAS Proteins The GRAS proteins are a family of plant specific proteins named

after GAI, RGA and SCR. Their C-termini show considerable sequence homology. The N-

terminal portion of each GRAS protein is highly divergent.

.GA 反应转录因子 , 在高等植物中结构高度保守，属于 GRAS 蛋白家族 .

DELLA Proteins as Integrators of Multiple Signals

GID1-mediated gibberellin signaling in plants

GA-INSENSITIVE DWARF1

YAB1

李天丰介绍

Characterization of the Molecular Mechanism Underlying Gibberellin Perception Complex Formation in Rice

Model for the Proteolysis-Independent Regulation of DELLA Repressor Activity.

GID1-mediated gibberellin signaling in plants

(Hirano et al., 2009)

(Nature Chemical Biology,2009,5:301-307)

Gibberellin signal transduction:cereal aleurone layers Gibberellic acid enhances the transcription of α-

amylase mRNA A GA-MYB transcription factor regulates α-amyla

se gene expression Gibberellin receptors may interact with G-protein

s on the plasma membrane Signaling intermediates

谢谢！