Leucine-rich repeat receptor-like kinases (LRR-RLKs), HAESA, ERECTA-family

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1 Leucine-rich repeat receptor-like kinases (LRR-RLKs), HAESA, ERECTA-family

2 GENES & DEVELOPMENT (2000) 14:

3 INTRODUCTION Flower Diagram

4 INTRODUCTION Abscission In plant, the process by which a plant drops one or more of its parts, such as a leaf, fruit, flower, or seed Cytoplasmically dense cells : Enlargement, accumulation of cell wall & pectin-degrading enzymes

5 INTRODUCTION Abscission Contribution of plant hormones : auxin delay abscission, ethylene promote abscission Mechanism 1. Ethylene-dependent pathway ex) etr1-1 (ethylene insensitive mutant) 2. Ethylene-independent pathway : intercellular response (protein phosphorylation mediated by transmembrane receptor protein kinase) RLKs (receptor-like protein kinases) - Function: Prevention of self-pollination, Pathogen response, Perception of hormones, Signaling, Plant development - Key regulator of plant development ; LRR-RLKs Ex) CLAVATA 1 : control proliferation and differentiation balance of the shoot & floral apical meristem ERECTA : control the organ shapes bri1 : perception of brassinosteroids hormones, signaling

6 Results HAESA - Arabidopsis RLK5 gene - Formerly name : RLK5 - HAESA meaning to stick to, adhere to, cling to ; Latin word, reflect its phenotype HAESA promoter activity is observed in the abscission zones. Receptacle (sepals, petals, stamens) GENES & DEVELOPMENT (2000) 14: Figure 1. HAESA expression pattern

7 Results 120kD * Antibody ; binds at different site - CAT (catalytic domain) - EXT (extracellular domain) - TAIL (catalytic-tail; carboxy-terminal 36 a.a) RLK5 unique - Pm (Plasma membrane-enriched) - Ms (total microsomal membrane) - Sol (soluble protein) - H + -ATPase : plasma membrane ATPase - a-tip : tonoplast intrinsic protein Figure 2. Subcellular immunolocalization of HAESA GENES & DEVELOPMENT (2000) 14: HAESA is a plasma membrane-localized protein

8 Results 120kD 85kD 65kD Autophosphorylated protein phosphoproteins HAESA protein size: 109kD 120kD autophosphorylation (Horn and Walker 1994) Figure 3. Immunoprecipitation and autophosphorylation of HAESA GENES & DEVELOPMENT (2000) 14: HAESA protein is a kinase that autophosphorylates on serine and threonin residues.

9 Results Figure 4. Antisense suppression of HAESA and floral organ abscission phenotype Figure 5. Loss of the transgene leads to loss of the floral organ abscission phenotype HAESA functions in developmentally regulated floral organ abscission GENES & DEVELOPMENT (2000) 14:

10 HAESA Receptor-like protein kinase Expression in the abscission zones where the sepals, petals, and stamens attach to the receptacle Plasma membrane serine/threonine protein kinase by protein kinase activity assays Reduction of function of HAESA (antisense construct) results in delayed abscission of floral organs HAESA functions in developmentally regulated floral organ abscission

11 Development (2004) 7:

12 INTRODUCTION ERECTA Highly expressed in the SAM(shoot apical meristem) & developing lateral organs mutant erecta has compact flower phonotype Encodes LRR-RLK (leucine-rich receptor like serine/threonine kinase) Mediates cell-cell signals that sense and coordinate organ growth

13 Results - ERECTA has exon-intron structure with 26 introns. Development (2004) 7: ERL1(At5g62230), ERL2(At5g07180) has 26 introns conserve the LRR region & kinase domain.

14 Results 1) Vegetative stage : shoot meristem, leaf primordia, juvenile leaves 2) Reproductive stage: young developing flowers ERECTA, ERL1, ERL2 display overlapping expression site. Development (2004) 7: Figure 3. ERECTA, ERL1, ERL2 are expressed in young proliferation tissues in an overlapping but unique manner

15 Results - ERL1, ERL2 act in an overlapping but distinct part of the ERECTA signaling pathway in regulating inflorescence architecture and organ shape Figure 5. ELR1&ERL2 genes are partially redundant and show synergistic interaction with ERCTA Development (2004) 7:

16 Results Figure 6. erecta-105 erl1-2 erl2-1 triple mutations lead to dramatically reduced plat growth, aberrant flower development, and reduced cell numbers in petals and pedicels - Similar transgenic erecta-105 plants - erecta erl1 erl2 are largely due to a decrease in cell number - ERECTA-family genes promote cell proliferation during organ growth Development (2004) 7:

17 ERECTA-family receptor like kinase ERL1 and ERL2, functional paralogs of ERECTA, play redundant but unique roles in a part of the ERECTA signaling pathway Synergistic interaction of three ERECTA-family RLKs in organ size erl1 and erl2 mutants enhanced erecta defects in unique manner The mutants defected lateral organ size and abnormal flower development, which are due to severely reduced cell proliferation ERECTA-family RLKs as redundant receptors that link cell proliferation to organ growth and patterning