Expression Profiling of FLOWERING LOCUS T-Like Gene in Alternate Bearing ‘Hass' Avocado Trees Suggests a Role for PaFT in Avocado Flower Induction

Abstract

In many perennials, heavy fruit load on a shoot decreases the ability of the plant to undergo floral induction in the following spring, resulting in a pattern of crop production known as alternate bearing. Here, we studied the effects of fruit load on floral determination in ‘Hass' avocado (Persea americana). De-fruiting experiments initially confirmed the negative effects of fruit load on return to flowering. Next, we isolated a FLOWERING LOCUS T-like gene, PaFT, hypothesized to act as a phloem-mobile florigen signal and examined its expression profile in shoot tissues of on (fully loaded) and off (fruit-lacking) trees. Expression analyses revealed a strong peak in PaFT transcript levels in leaves of off trees from the end of October through November, followed by a return to starting levels. Moreover and concomitant with inflorescence development, only off buds displayed up-regulation of the floral identity transcripts PaAP1 and PaLFY, with significant variation being detected from October and November, respectively. Furthermore, a parallel microscopic study of off apical buds revealed the presence of secondary inflorescence axis structures that only appeared towards the end of November. Finally, ectopic expression of PaFT in Arabidopsis resulted in early flowering transition. Together, our data suggests a link between increased PaFT expression observed during late autumn and avocado flower induction. Furthermore, our results also imply that, as in the case of other crop trees, fruit-load might affect flowering by repressing the expression of PaFT in the leaves. Possible mechanism(s) by which fruit crop might repress PaFT expression, are discussed.

A possible role for flowering locus T‐encoding genes in interpreting environmental and internal cues affecting olive (Olea europaea L.) flower induction

“…) and avocado (Ziv et al . ), flower induction in olives occurs at a time when, normally, no fruit are present on the tree. The nature of this ‘biochemical memory’ is unknown to us, yet its outcome may be through OeFT and OeTFL1‐1 gene expression.…”

“…Although not yet tested in olive, in other fruit trees, there is growing evidence that HFL directly inhibits flower induction (Nakagawa et al 2012;Nishikawa et al 2012;Samach and Smith 2013;Ziv et al 2014;Haberman et al 2016). In any case, in olive, a branch with HFL will not initiate inflorescences the following winter and will thus carry no fruit the following summer.…”

“…The accumulation of FT-like gene transcripts has been documented as preceding flower initiation in several fruit trees, such as citrus (Nishikawa et al 2007;Muñoz-Fambuena et al 2011;Shalom et al 2012), mango (Mangifera indica L.) (Nakagawa et al 2012), avocado (Persea americana Mill.) (Ziv et al 2014) and apple (Malus domestica Borkh.) (Kotoda et al 2010).…”

Ecological speciation in sympatric palms: 1. Gene expression, selection and pleiotropy

“…Corroboration of these results using further model plant systems, for example rice, would increase support for the generality of these gene functions and support the argument that these loci have similar functions in palms. However, it has already been shown that much of the core flowering time control system is conserved across widely diverged species, with measurable phenotypic effects as a result of transferring genes from monocot to dicot (rice to potato; Navarro et al ., ), perennial to annual and vice versa ( Arabidopsis to and from Populus ; Peña et al ., ), tropical to temperate (avocado to Arabidopsis ; Ziv et al ., ), and photoperiodic to nonphotoperiodic species (tomato to Arabidopsis ; Ben‐Naim et al ., ). There is more interspecific variation in abiotic stress responses, but there are still numerous conserved genes and pathways for drought and salinity tolerance between taxonomically diverse groups such as angiosperms and bryophytes (Cuming et al ., ; Pareek et al ., ; Wang et al ., ).…”

NUTRITIONAL AND HORMONAL FACTORS AFFECTING FRUIT SET IN AVOCADO (Persea americana Mill.)

“…Currently these hypotheses have been overtaken by the demonstration that in the years "on" the fruit suppresses the expression of the gene ortholog FLOWERING LOCUS T, PaFT (Ziv et al, 2014) from the end of October to the end of November, and only in the buds of the trees "off" is an expression of the floral identity transcripts PaAP1 and PaLFY, with significant variations detected since…”