Plant development III - Plants develop throughout their life

Question 1

Embryo development of
angiosperms

Answer 1

zygote proceeds though series of transverse and longitudinal divisions that establish axial and radial polarity.

Question 2

Describe mutant use to study embryo development

Answer 2

• mutants that produce seedlings that lack part of the plant body can be used to infer genetic control over the embryonic development of plant organs.

Question 3

Describe gene modification

Answer 3

indels and substitution can determine loss of function, acquisition of a new one or abolish protein translation

Question 4

Describe the early embryo establishment of polarity

Answer 4

• established by vacuole/nuclear positioning
• transmitted to the multicellular embryo via asymmetric division
• at the 2-cell stage, polarity is maintained by auxin fluxes

Question 5

Describe the radial development of the embryo

Answer 5

auxin induces periclinal divisions that establish radial expansion, which shifts from sink to source of auxin through the activation of biosynthetic and transport genes

Question 6

Describe the molecular control of SAM and RAM activity

Answer 6

• marked already in the embryo by the expression homeotic genes

Question 7

Describe some homeotic genes

Answer 7

Wuschel and WOX

Question 8

Describe WUS

Answer 8

• expressed in the OC of the SAM
• diffuses to the upper layers

Question 9

OC

Answer 9

organizing centre

Question 10

Describe the WUS signalling pathway

Answer 10

• CLV3
• CLV1/CORYN

Question 11

Describe how the WUS signalling pathway was elucidated

Answer 11

identification of mutants with increased inflorescence and flower organ size

Question 12

CLV3

Answer 12

CLAVATA3

Question 13

Describe WUS and the CLAVATA genes

Answer 13

• regulate each other (in a cell non-autonomous manner)
• establish domains: the Organizing Centre and Stem Cell pool

Question 14

Describe CLV3 and CLV1

Answer 14

• CLV3: peptide hormone
• CLV1: receptor

Question 15

Describe gene expression in plant development

Answer 15

• secreted peptides produced via translation and subsequent proteolytic trimming and additional modifications perceived by membrane receptors
• initiate a phosphorylation cascade that affects gene expression

Question 16

Describe some modifications

Answer 16

• sulfylation
• hydroxylation

Question 17

Describe peptide activation

Answer 17

series of protease hydrolyses

Question 18

Describe the stm mutation

Answer 18

• prevents SAM maintenance
• partly due to the activation of cytokinin biosynthesis (via the IPT gene)

Question 19

stm

Answer 19

§shoot meristemless

Question 20

Describe the production of primordia from the SAM

Answer 20

• ARP genes specify primordial identity and exclude STM expression,
• in the central zone STM prevents ARP expression

Question 21

Describe ARP proteins

Answer 21

• transcription factors
• control primordium identity

Question 22

Describe primordia localisation

Answer 22

• depends on the existing primordia
• activator is depleted around the primordium
• PINs canalise auxin towards the apex of the primordial

Question 23

Describe pin mutants

Answer 23

• fails to create primordia
• local auxin application (shown through red fluorescent staining) induces production of a new leaf primordium

Question 24

Describe primordia budding

Answer 24

• depends on auxin distribution
• PINs inactivate STM expression
• promotes proliferation and expression of ARP genes

Question 25

Describe the molecular determination of leaf shape

Answer 25

- PIN directs auxin to form a maximum that precedes bud outgrowth - KNOX genes promote leaflet and lobe production - leaf complexity based on outgrowths is determined by the establishment of auxin maxima

Question 26

In which plant are KNOX genes studied?

Answer 26

Cardamine hirsuta

Question 27

What establishes auxin maxima?

Answer 27

PIN proteins

Question 28

Describe the establishment of leaf polarity

Answer 28

- removal of L1 layers of cells in the primordium (abaxialisation) - deletion KANADI in the primordium (adaxialisation) - intermediate layer of WOX expression genes required for leaf blade expansion

Question 29

KANADI

Answer 29

MYB gene

Question 30

Describe establishment of leaf polarity in snapdragon

Answer 30

genetic inactivation of PHANTASTICA causes complete abaxialization.

Question 31

PHANTASTICA

Answer 31

HD-ZIP III gene

Question 32

Describe development of the RAM

Answer 32

- main cell types of the RAM are present in the embryo - post-germination, RAM undergoes rapid expansion - subsequently balanced by the cell expansion rate

Question 33

Describe molecular regulation of the RAM

Answer 33

- PLETHORA TFs regulate RAM identity partly by directing auxin synthesis and transport in the RAM - signaling peptides specify WOX5 activity in the QC that prevents differentiation of root cap cells - gradients

Question 34

Describe the gradients that regulate the RAM

Answer 34

- diffusible small RNAs - auxin - diffusible TFs - signaling peptide gradients

Question 35

Describe the diffusible small RNAs that regulate the RAM

Answer 35

microRNA165/166 target HD-ZIP III TFs

Question 36

Describe the auxin gradients that regulate the RAM

Answer 36

- local IAA synthesis - transporters: PIN efflux carriers, influx carriers

Question 37

Describe the diffusible TFs that regulate the RAM

Answer 37

- GRAS type TFs - WOX-type TFs

Question 38

Describe the signalling peptide gradients that regulate the RAM

Answer 38

- transcription/translation - post-translational modification - export

Question 39

Describe cell elongation in the elongation zone

Answer 39

- cell wall modifying enzymes relax the cell wall - needs pressure turgor produced by water uptake in the vacuole - direction constraints by cellulose fibrils place growth perpendicularly to the growth axis

Question 40

Give a class of cell wall modifying enzymes

Answer 40

expansins

Question 41

Describe aquaporins

Answer 41

tonoblast intrinsic proteins

Question 42

Describe the differentiation zone

Answer 42

- nutrients and water are taken up by root hairs - localised in the proximity of the RAM - travel to the xylem via the apoplast and the symplast

Question 43

apoplast

Answer 43

cell wall system

Question 44

symplast

Answer 44

cytoplasm system

Question 45

Describe the root stele

Answer 45

- above the hair zone - impermeabilised by suberin enrichment in the cell walls and lignin deposition - forms the Casparian strip

Question 46

Describe the specification of root hair fate in the epidermis

Answer 46

diffusible signal coming from edges of cortex cells

Question 47

Describe the Casparian strip

Answer 47

- lignification in a belt along the endodermis - ensured by localised deposition and polymerization of monolignols - directed by CASP proteins.

Question 48

Describe monolignol depositou and polymerisation

Answer 48

peroxidase and NADPH oxidases

Question 49

Describe lateral root development

Answer 49

- pericycle cells determined by auxin peaks at intervals become initials of LRPs - activated at distance in the differentiation zone

Question 50

pericycle

Answer 50

External cells of the stele

Question 51

LRPs

Answer 51

lateral root primordia

Question 52

Describe formation of the LRP

Answer 52

- auxin maxima direct anticlinal and periclinal cell divisions - auxin export in the above-laying cells softens their cell walls to enable penetration and emergence of the lateral root

Question 53

Most meristem types of a plant are

Answer 53

already specified in the mature embryo of angiosperms

Question 54

* Molecular gradients (hormones, peptides, RNAs and proteins) establish functional domains that exclude each other * Shoot and root development mainly require concerted auxin and cytokinin activity * Leaf complexity and root meristem maintenance depend on the establishment of auxin maxima * Leaf and root patterning requires the intertwined activity of a large number of transcriptional regulators