Fruit load induces changes in global gene expression and in abscisic acid (ABA) and indole acetic acid (IAA) homeostasis in citrus buds.
Many fruit trees undergo cycles of heavy fruit load (ON-Crop) in one year, followed by low fruit load (OFF-Crop) the following year, a phenomenon known as alternate bearing (AB). The mechanism by which fruit load affects flowering induction during the following year (return bloom) is still unclear. Although not proven, it is commonly accepted that the fruit or an organ which senses fruit presence generates an inhibitory signal that moves into the bud and inhibits apical meristem transition. Indeed, fruit removal from ON-Crop trees (de-fruiting) induces return bloom. Identification of regulatory or metabolic processes modified in the bud in association with altered fruit load might shed light on the nature of the AB signalling process. The bud transcriptome of de-fruited citrus trees was compared with those of ON- and OFF-Crop trees. Fruit removal resulted in relatively rapid changes in global gene expression, including induction of photosynthetic genes and proteins. Altered regulatory mechanisms included abscisic acid (ABA) metabolism and auxin polar transport. Genes of ABA biosynthesis were induced; however, hormone analyses showed that the ABA level was reduced in OFF-Crop buds and in buds shortly following fruit removal. Additionally, genes associated with Ca(2+)-dependent auxin polar transport were remarkably induced in buds of OFF-Crop and de-fruited trees. Hormone analyses showed that auxin levels were reduced in these buds as compared with ON-Crop buds. In view of the auxin transport autoinhibition theory, the possibility that auxin distribution plays a role in determining bud fate is discussed.
Department of Fruit Trees Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Liron
L
Shalom
Department of Fruit Trees Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Sivan
S
Samuels
Department of Fruit Trees Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel.
Naftali
N
Zur
Department of Fruit Trees Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel.
Lyudmila
L
Shlizerman
Department of Fruit Trees Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel.
Adi
A
Doron-Faigenboim
Department of Plant Sciences, University of California, Davis, CA 95616, USA.
Eduardo
E
Blumwald
Department of Fruit Trees Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel vhasadka@volcani.agri.gov.il.
Avi
A
Sadka
D000040:Abscisic Acid / Q000378:metabolism*; D002957:Citrus / Q000235:genetics* / Q000378:metabolism; D035264:Flowers / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant; D059014:High-Throughput Nucleotide Sequencing; D006706:Homeostasis; D007210:Indoleacetic Acids / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D017423:Sequence Analysis, RNA; D059467:Transcriptome; D014197:Trees
D007210:Indoleacetic Acids; C030737:indoleacetic acid; D000040:Abscisic Acid
Abscisic acid; alternate bearing; auxin; bud; citrus; flowering; fruit load.