Physiogenomics of European Pear Ripening (Pyrus communis L.)

Most European pear fruit genotypes exhibit putative requirements for cold-temperature exposure to acquire competency for System 2 ethylene biosynthetic induction.  Understanding of System 2-specific and type III ACS expression during tree fruits' System 1-to-System 2 transition remains unclear.  We utilized a physiologically-guided model of 'Bartlett' and 'D'Anjou' pear conditioning to capture changes in gene expression among 8 phytohormone, secondary messenger and respiration-related pathways at equal intervals of conditioning and ripening.  In this study, 'Bartlett' pear require 2 weeks at 0°C while 'D'Anjou' require 2 months at 0°C. Nonmetric multidimensional scaling (NMDS) and linear models of statistical analysis were employed to identify variation of gene expression by pear cultivar, conditioning treatment and fruit phenology through the study.  Results suggest different rates of acquisition of ripening competency during conditioning, depending on storage temperature.  This may be related to observed differential expression of abscisic acid-related (ABA), auxin-responsive, and respiration-related transcripts by cultivar, conditioning treatment, and during fruits' progression through the study.  Our work suggests that increased conditioning requirements in 'D'Anjou' may be correlated to reduced ABA accumulation in tissues due (in part) to unique ABA biosynthetic and degrading (respectively) NCED1 -like, CYP707A-like expression.  Additionally, differential expression of AOX1- and 2-like genes was observed by cultivar and conditioning treatment.  Together these results demonstrate that additional pathways beyond ethylene signaling influence climacteric fruits' transition to System 2 ethylene biosynthesis in response to cold-temperatures. These pathways are signatures of underlying biology from which chemical and physiological postharvest management strategies can be generated. (Pyrus communis L.)