1. Inoculation of tomato plants with rhizobacteria enhances the performance of the phloem-feeding insect Bemisia tabaci
Roee Shavit1,2, Maya Ofek-Lalzar3, Saul Burdman2 and Shai Morin1
1Department of Entomology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
2Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
3Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization of Israel, Bet Dagan, Israel.

2. Two forms of induced resistance that are systemically expressed in the plant
SAR
ISR
Callose deposition
Enhanced expression of JA/ET-responsive genes
Pseudomonas fluorescens WCS417r
et al,. 2009) (Pieterse
Pieterse et al., Nature Chemical Biology, 2009

3. Hypothesis and complexity
As JA/ET are key regulators of both ISR and plant defenses against herbivorous insects, it has been hypothesized that ISR induced by PGPR should benefit plants in their battle against insect herbivores.
Indeed, studies with A. thaliana plants that were pre-inoculated with the PGPR P. fluorescens WCS417r showed that the growth and development of the generalist caterpillar Spodoptera exigua was negatively affected by the PGPR treatment (Van Oosten et al. 2008).
However, it was recently found that P. fluorescens WCS417r has a positive effect on the performance (weight gain and intrinsic rate of increase) of the generalist phloem-feeding aphid Myzus persicae on A. thaliana (Pineda et al., 2012).

4. Bemisia tabaci
Broad host range, extending over 600 plant species from over 70 plant families including many crop species

5. A. thaliana defense responses to B. tabaci
Arabidopsis mutants
SA JA
SA JA
Higher nymphal development
Lower nymphal development
Kempema et al., Plant physiology 143:
Zarate et al., Plant physiology 143:

6. Tomato defense responses to B. tabaci
Gene Protein Pathway
Puthoff et al. (J. Chem. Ecol., 2010, 36:1271–1285)

7. Control plants, not inoculated with P. fluorescens and without B
Control plants, not inoculated with P. fluorescens and without B. tabaci infestation (P-/B- plants)
P. fluorescens pre-inoculated plants without B. tabaci infestation (P+/B- plants)
Non-inoculated plants with B. tabaci infestation (P-/B+ plants);
P. fluorescens pre-inoculated plants with B. tabaci infestation (P+/B+ plants).
We hypothesized that the relationship between the players in the B. tabaci - tomato - P. fluorescens system will add a general perspective to the complexity reported for the M. persicae - A. thaliana - P. fluorescens system.

8. Reproductive performance of B. tabaci on P
Reproductive performance of B. tabaci on P. fluorescens WCS417r pre-inoculated and non-inoculated tomato plants * *
N.S.

9. Salicylic Acid Pathway Jasmonic Acid/Ethylene Pathways
The expression level of SA and JA/ET responsive genes transcripts in tomato before and after B. tabaci infestation
Salicylic Acid Pathway
Jasmonic Acid/Ethylene Pathways SA ET JA
PR5
PR2
כעת נעבור לאיפיון המולקולרי של רמות ה-SA ו-JA בצמחי הטבק. איפיון זה נעשה באמצעות בחינת רמת הביטוי של מספר גנים במסלולים הללו ע"י Real time PCR.
במסלול ה- SA בדקנו את הגן PR1a – pathogenesis related1a שמעורב באינדוקציית תגובת ההגנה הסיסטמית של הצמח כנגד מגוון רחב של פתוגנים.
במסלול ה-JA בדקנו שני גנים: 1. הגן AOC – allene oxide cyclase: מעורב בביוסינטזה של JA.
2. הגן COI1 – coronative insensitive 1: מעורב באקטיבציה של תגובת ההגנה עצמה של הצמח (שמתווכת על-ידי (JA.
רמת הביטוי של הגנים הללו נבדקה בצמחי ה-WT וגם בצמחים הטרנסגניים ללא פציעה ולאחר פציעה של 8 שעות, 48 שעות ולאחר 5 ימים.
[המסלולים הללו הם בארבידופסיס ובטבק לא כל הגנים קיימים למשל: PDF1.2 ו-VSP1].
PI2
PI1
‘Day 0' (before B. tabaci infestation)
‘Day 1' (the effect of 24h of adults' feeding and egg laying)
‘Day 6' (the beginning of egg hatching, minimal infestation effect)
‘Day 12' (presence of B. tabaci 2nd and 3rd feeding nymphs)

10. The expression level of SA and JA/ET responsive genes transcripts before and after B. tabaci infestation ?
JA/ET
JA/ET
JA/ET SA
Adults
Eggs
II,III Instars

11. Denaturing gradient gel electrophoresis (DGGE) profiles of the bacterial communities of the tomato rhizosphere

12. Cluster analysis of tomato rhizosphere bacterial community patterns
Time P =
Bacteria P = 0.015
Insect P = 0.38
Group III –
Non-inoculated, infested and un-infested plants (‘day 12’)
Group II –
Pre-inoculated, infested (‘day 12’) and un-infested (‘day 0‘, ‘day 12’) plants
Group I –
Non-inoculated plants before infestation (‘day 0’)

13. The levels, in P. fluorescens WCS417r pre-inoculated and non-inoculated plants of soluble carbohydrates, N (nitrogen), and C (carbon)

14. Why do generalist phloem feeders respond differently than other insect herbivores to pre-inoculation of plant hosts with P. fluorescens WCS417r?

15. Alternative explanations
Down-regulation of both ET-responsive genes and JA-responsive genes (to a lesser extent) in P. fluorescens WCS417r pre-inoculated plants (suppressed expression of both ABA1 and MYC2 in plants infested with M. persicae or PI-I, PI-II and PR-2 in plants infested with B. tabaci).
A possible manipulation by P. fluorescens of the plant quality (in terms of suitability for B. tabaci) through an indirect effect on the rhizosphere bacterial community (suppression of the activity of pathogenic and non-pathogenic microorganisms by microbial antagonism).
Root colonization by P. fluorescens WCS417r seems not to promote tomato growth or nutrient uptake directly.

16. Israel Science Foundation
Yissumit A – ( )
Yissumit B - ( )
Israel Science Foundation