Suppression of sucrose synthase affects auxin signaling and leaf morphology in tomato

<div><p>Metabolic enzymes have been found to play roles in plant development. Sucrose synthase (SUS) is one of the two enzyme families involved in sucrose cleavage in plants. In tomato, six SUS genes have been found. We generated transgenic tomato plants with RNAi suppression of <i>SlSUS1</i>, <i>SlSUS3</i> and <i>SlSUS4</i> genes. Independent transgenic lines with RNAi suppression of more than one <i>SUS</i> gene exhibited morphological effects on their cotyledons and leaf structure, but there were no significant effects on their carbohydrate levels, demonstrating that SUS has a developmental function, in addition to its metabolic function. Shoot apices of the transgenic lines showed elevated expression of <i>JAGGED</i> (<i>JAG</i>) and the auxin transporter <i>PIN1</i>. In a PIN1-GFP fusion reporter/SUS-RNAi hybrid, PIN1-GFP patterns were altered in developing leaves (as compared to control plants), indicating that <i>SlSUS</i> suppression alters auxin signaling. These results suggest possible roles for SUS in the regulation of plant growth and leaf morphology, in association with the auxin-signaling pathway.</p></div

Effect of <i>SlSUS</i> suppression on tomato fertility and seed viability.

<p><b>(A)</b><i>SlSUS-RNAi</i> and WT plants were grown in a greenhouse to maturity. Flowers from the first five inflorescences from the ground of each plant (<i>n</i> = 9) were counted. <b>(B)</b> Fruit set was calculated as the number of fruit divided by the number of flowers from the first five inflorescences of each plant (<i>n</i> = 9). <b>(C)</b> To calculate average seed weights, 50 seeds per fruit (<i>n</i> = 4) were counted and weighed, and that weight was divided by the number of seeds. Error bars represent the standard error. Asterisks indicate a statistically significant difference relative to the WT (* <i>P</i> < 0.05; ** <i>P</i> < 0.01).</p

Short De-Etiolation Increases the Rooting of VC801 Avocado Rootstock

Dark-grown (etiolated) branches of many recalcitrant plant species root better than their green counterparts. Here it was hypothesized that changes in cell-wall properties and hormones occurring during etiolation contribute to rooting efficiency. Measurements of chlorophyll, carbohydrate and auxin contents, as well as tissue compression, histological analysis and gene-expression profiles were determined in etiolated and de-etiolated branches of the avocado rootstock VC801. Differences in chlorophyll content and tissue rigidity, and changes in xyloglucan and pectin in cambium and parenchyma cells were found. Interestingly, lignin and sugar contents were similar, suggesting that de-etiolated branches resemble the etiolated ones in this respect. Surprisingly, the branches that underwent short de-etiolation rooted better than the etiolated ones, and only a slight difference in IAA content between the two was observed. Gene-expression profiles revealed an increase in ethylene-responsive transcripts in the etiolated branches, which correlated with enrichment in xyloglucan hydrolases. In contrast, transcripts encoding pectin methylesterase and pectolyases were enriched in the de-etiolated branches. Taken together, it seems that the short de-etiolation period led to fine tuning of the conditions favoring adventitious root formation in terms of auxin&ndash;ethylene balance and cell-wall properties

Expression patterns of the three <i>SlSUS</i> genes in young stems.

<p>Comparative GUS stains of stems from tomato lines expressing GUS under the control of each of the three <i>SlSUS</i> promoters (<i>proSlSUS</i>). Leftmost column: whole stem segment, bar– 1 mm; second column from left: magnifications of leftmost panels, showing axillary shoots (arrows), bar– 0.5 mm; third column from left: micrographs of stem cross-sections, bar– 0.5 mm; rightmost column: magnification of boxed areas from previous panels; EP–external phloem; IP–internal phloem; XY–xylem vessel members; bar– 0.1 mm.</p

<i>SlSUS-RNAi</i> lines exhibit <i>SlSUS</i> co-suppression.

<p><b>(A-C)</b> Reduced expression of <i>SlSUS</i> genes. RNA was extracted from green fruits, shoot apices, and mature leaves of <i>SlSUS-RNAi</i> and WT lines. cDNA was generated and subjected to real-time PCR analysis, using primers specific for <i>SlSUS1</i>, <i>3</i> and <i>4</i>. Cyclophilin was used as a reference gene. Error bars indicate the standard error (<i>n</i> ≥ 3). Asterisks indicate a statistically significant difference from the WT (* <i>P</i> < 0.05; ** <i>P</i> < 0.01).</p

The S1R4 line exhibits abnormal leaf morphology.

<p><b>(A)</b> Mature S1R4 leaf, <b>(B)</b> mature WT leaf, <b>(C)</b> magnification of the boxed areas in the S1R4 leaf, <b>(D)</b> magnification of the boxed areas in the WT leaf and <b>(E)</b> close-ups of the adaxial and <b>(F)</b> the abaxial side of an S1R4 leaf, showing ectopic blade formation of the leaflets (red area). Note the angle of the petiolules (arrowheads) and of the leaflet curling (arrow). Bar– 2 cm.</p

Honey bee (Apis mellifera) strains differ in avocado (Persea americana) nectar foraging preference

Avocado nectar is unusual because it contains perseitol, a 7-carbon sugar alcohol. We compared avocado-nectar collection by commonly used Italian-based (IT) honey bee colonies and New World Carniolan (NWC) colonies introduced in avocado orchards in Israel (IS) and California (CA). In IS, NWC colonies had greater honey yields (1.2–4.3 fold), with a higher perseitol content (1.1–5.4 fold), than IT colonies. Overall, we calculated that NWC bees collected 1.4 to 18.1 times more avocado nectar than IT bees in the IS orchards. In CA, analyses of the crop contents of foragers revealed non-significant strain-specific trends in visitation to avocado flowers that were consistent with those indicated by data from IS. The genetic basis for honey bee differences in visitation to avocado flowers was further supported by the consistently high honey perseitol content of selected colonies over two years. The implications of possible strain-specific difference in avocado-nectar preference are discussed in relation to the use of honey bees for avocado pollination

Auxin transport is altered in leaf primordia of SlSUS-suppressed plants.

<p><b>(A, B)</b> Shoot apices and the youngest leaf primordia; ap–apex; fl–inflorescence primordium; indented arrowhead–normal PIN1 distribution along the center line of the primordium; flat arrowhead–ectopic distribution of PIN1 on the adaxial side of S1R4 primordium. <b>(C, D)</b> Leaflet primordia in older leaf primordia. Normal auxin transport proceeds along the periphery of the primordium (white arrows) with an auxin maximum at the apex (asterisk) and then flows through the center line (yellow arrows) along the path of the future vascular tissue. In the S1R4 primordium, transport is disorganized (dashed arrows with dashed lines) and the positions of the apex and centerline are altered. Bar– 100 μm.</p

<i>SlSUS</i> suppression does not significantly affect soluble sugars or starch content.

<p><b>(A)</b> Sucrose, glucose and fructose contents of young green fruit. <b>(B)</b> Starch content of young green fruit. <b>(C)</b> Starch content of mature leaves. Error bars indicate standard error (<i>n</i> = 5).</p