A proposed conserved role for an avocado fw2.2-like gene as a negative regulator of fruit cell division

Abstract

Previous studies using 'Hass' avocado and its small fruit (SF) phenotype as a model showed that SF is limited by cell number, not by cell size. In an attempt to explore the molecular mechanisms regulating avocado fruit cell division, we isolated four distinct avocado cell proliferation-related genes and investigated their expression characteristics, comparing normal fruit (NF) and SF developmental patterns. Three cDNAs termed PaCYCA1, PaCYCB1 and PaPCNA, encoding two mitotic cyclins and a proliferating cell nuclear antigen (PCNA), were first isolated from young NF tissues. The accumulation of their transcripts was predominant in mitotically active organs, including young fruitlets, leaves and roots. Furthermore, a fourth full-length cDNA, designated Pafw2.2-like, encoding a FW2.2 (fruit-weight)-like protein, was isolated from SF tissues. FW2.2 is postulated to function as a negative regulator of cell division in tomato fruit. Remarkably, northern analysis revealed that the accumulation of the mitotic cyclins and of PCNA transcripts gradually decreased in NF tissues during growth, whereas in SF, their levels had already decreased at earlier stages of fruit development, concomitant with an earlier arrest of fruit cell division activity. In contrast, parallel sq-RT-PCR analysis showed that Pafw2.2-like mRNA accumulation was considerably higher in SF tissues than in the same NF tissues essentially at all examined stages of fruit growth. Together, our data suggest essential roles for the two mitotic cyclins genes and the PCNA gene in regulating avocado fruit development. Furthermore, the possibility that Pafw2.2-like acts as does fw2.2 in tomato, is discussed.

Differences in Physiological Characteristics and Gene Expression Levels in Fruits between Japanese Persimmon (<i>Diospyros kaki</i> Thunb.) ‘Hiratanenashi’ and Its Small Fruit Mutant ‘Totsutanenashi’

“…The differences in unigene number and length between our results and Luo et al (2014) are probably due to the different sequencing strategies, that is, the sample preparation, sequencing platforms and assembly programs. It was reported that the expression level of Pafw2.2-like was higher in smaller fruits than in normal fruits of 'Hass' in avocado (Cowan et al, 1997;Dehan et al, 2010;Zilkah and Klein, 1987). FW2.2/CNR family genes are known to be associated with the regulation of fruit cell number in tomato (Frary et al, 2000) and sweet cherry (De Franceschi et al, 2013).…”

“…The FW2.2/CNR family of genes controls organ size by modulating cell numbers in other plant species such as avocado (Persea americana Mill. ; Dehan et al, 2010) and sweet cherry (De Franceschi et al, 2013). In avocado, the expression level of Pafw2.2-like was higher in the smaller fruits of 'Hass' trees than in normal fruits (Cowan et al, 1997;Dehan et al, 2010;Zilkah and Klein, 1987).…”

“…; Dehan et al, 2010) and sweet cherry (De Franceschi et al, 2013). In avocado, the expression level of Pafw2.2-like was higher in the smaller fruits of 'Hass' trees than in normal fruits (Cowan et al, 1997;Dehan et al, 2010;Zilkah and Klein, 1987). In sweet cherry, De Franceschi et al (2013) reported that PavCNR12, a CNR gene, is located within the confidence interval of the major fruit size G2 quantitative trait loci, which is postulated to affect fruit size by controlling mesocarp cell numbers , thereby, controlling fruit size (Olmstead et al, 2007).…”

Overexpression of OsDPR, a novel rice gene highly expressed under iron deficiency, suppresses plant growth

“…Following successful germination, plant growth depends on a combination of two essential processes; cell division and cell expansion. These two processes play essential roles in the determination of plant size [13]. The growth-limiting effects of various kinds of stress have been related to their effects on the regulation of elongation and cell division [10].…”

Evolution of FW2.2-like (FWL) and PLAC8 genes in eukaryotes

“…Interestingly, silencing of GmFWL1 expression resulted in greater condensation of cellular chromatin. Other, more distantly related FWL gene family members include PaFWL, 10 shown to regulate avocado fruit development. Other family members have been implicated as regulators of calcium influx (AtMCA1 11,12 ), as of the number and location of cysteine residues, FWL and PLAC8 core domains share similar tertiary structures and potentially similar biochemical functions.…”