S1-bZIPs play essential roles in plant growth and development, especially seed maturation, root growth, and flower development . For example, the transcript abundance of AtbZIP53 is markedly induced during the late stages of seed development . AtbZIP53 enhances the gene expression associated with seed maturation by specific heterodimerization with group C-bZIPs . AtbZIP11 and AtbZIP44 play a role in embryogenesis. AtbZIP44 shows high transcript levels at the early stage of seed development and is involved in micropylar endosperm loosening and seed coat rupture via its interaction with the promoter of AtMAN7 . The atbzip44 knock-out mutant shows slower germination and reduced expression of AtMAN7 . In Populus, the binding of poplar bZIP53 to the promoter of IAA4-1 and IAA4-2 inhibits adventitious root development . In horticultural plants, three S1-bZIP members are highly expressed in grape seed , but their regulatory mechanisms have yet to be elucidated. For example, CsbZIP-06 is highly expressed in female cucumber flowers and ovaries . Transgenic lines over expressing mORF of BZI-4 show reduced flower size and impaired pollen development . Over expressing AtbZIP1, AtbZIP53, tbz17, MusabZIP53, and FvbZIP11 shortened internode length, and stunted vegetative growth . FabZIPs1.1 and FvbZIP11 have been shown to be involved in fruit ripening in strawberry . Banana MabZIP91 and MabZIP104, large pots plastic which belong to S1-bZIP subgroup, showed high transcript abundance during fruit development and ripening .
These studies illustrate the various roles of S1-bZIPs as a regulator of plant growth and development .The S1-bZIP subgroup, with their functional diversity in all plants, reflects their importance as regulators. The literature covered in this review suggests that the small but unique and crucial S1-bZIP transcription factors play essential roles in the balance of carbon and amino acid metabolism, plant growth and development, and stress responses . S1-bZIPs also play important roles in regulating fruit quality and stress response. Through heterodimerization with group C-bZIPs, S1- bZIPs orchestrate an array of downstream transcriptional and metabolic control. However the C group bZIP dimerization partners of many S1-bZIPs have yet to be identified. The S1- bZIPs regulate sugar signaling and amino acid metabolism under energy-deprived conditions, which involves the Sucrose Induced Repression of Translation mechanism of the uORFs and through interaction with the SnRK1 pathway. However, further research is needed to explore whether and how SnRK1 and TOR kinase interact with C- and S1-bZIPs complex. The SC-uORF negatively regulates the translation of S1-bZIP mORFs and, in turn, downstream targets of the S1-bZIPs, which further affect fruit quality and other metabolite biosynthesis. Evidence suggests that over expression of S1-bZIP mORFs significantly increased the fruit sugar content and sweetness, showing the potential for improvement of fruit quality .
In addition, functional diversity and specificity among the S1-bZIPs need to be further defined. Using substitution of conserved amino acid residues in the DNA-binding domain could be a useful approach to clarify specific interconnections among S1-bZIPs and their dimerization partners in horticultural plants . Using CRISPR technology to create indel mutations in uORF start codons or enhancing the expression of S1-bZIPs using fruit specific promoters could provide broad applications to control the levels of sucrose and other nutrients for the improvement of the quality of fruits, vegetables, and flowers, and to improve stress response without the detrimental effects on plant growth and development in horticultural plants .A thorough investigation of primate diets, and how primates alter their diets in response to variation in food availability, is fundamental for understanding primate behavior, ecology and morphology. Periods of resource scarcity may have particularly important impacts on primate fitness because during these times feeding competition can be intense and food quality poo. While such periods can have disproportionate impacts on primate feeding adaptations and sociality, they occur infrequently in some environments. Long-term observations of primate feeding behavior and concurrent assessment of plant food availability are therefore necessary to sample across the full range of variation within the diet and to encompass periods of high and low resource availability. The need for long-term data sets is particularly acute in Southeast Asia because most forest types there exhibit dramatic, supra-annual fluctuations in fruit production that exceed the magnitude of variation in food availability characteristic of other tropical forests.
Mast fruiting events are periods of super-abundance of resources, and are characteristically followed by periods of extreme food scarcity. These phenological cycles are linked to EL Niño Southern Oscillation events and consequently occur at irregular intervals that are unpredictable from the perspective of vertebrate frugivores. Due to the hyper-variability in food availability in the Dipterocarp forests of SE Asia, dietary changes in response to food availability can be dramatic, with some primate species incurring negative energy balance during periods of low resource availability. Studying the responses of frugivores to these fluctuations in food availability—especially the responses of multiple taxa that differ in their dietary adaptations, life histories, and feeding strategies–can shed light on the evolution of primate feeding adaptations. A useful way to understand dietary responses to fluctuations in food availability is to categorize dietary items based on their use and availability, and in particular to distinguish between preferred and fallback foods . Preferred foods are generally high-quality foods that are easy to process and are eaten more often than would be predicted based on their availability. Foods that are consumed more during periods when preferred foods are scarce are termed fallback foods. Comparative studies of primate diets are particularly informative for understanding how responses to resource availability drive evolutionary processes. For example, the African grey-cheeked mangabey has a relatively high degree of dietary overlap with the sympatric red-tail guenon . L. albigena possesses much harder tooth enamel than C. ascanius, some of the hardest tooth enamel found in extant primates. The foods that L. albigena consumes during times of resource scarcity are thicker and harder to process than foods eaten by C. ascanius, and the difference in tooth enamel thickness between the two species can be explained by the foods they consume when resources are scarce. Comparative studies can also be useful for understanding how resource availability influences primate population biology. For example, the population density of white-bearded gibbons is limited by the availability of their fallback foods, whereas red leaf monkey population density is limited by the availability of high quality, preferred foods; these differences may be due to differences in the life histories of the two species. Gibbons and leaf monkeys provide an excellent comparison for investigating the effects of resource variability on primate ecology because they are similar in body size, but have different social systems, life histories and diets. Gibbons generally live in male-female pairs and have relatively slow life histories , whereas leaf monkeys live in single-male, multi-female groups and have relatively fast life histories. Gibbons and leaf monkeys are classified as frugivores and folivores/gramnivores, respectively. Gibbons are generally considered ripe-fruit specialists and possess few morphological adaptations to process low-quality foods, whereas leaf monkeys, like all colobine monkeys, have morphological adaptations such as complex, multi-chambered stomachs, thin tooth enamel and high shearing cusps that facilitate the consumption of leaves. In this study, we conduct a dietary analysis of two sympatric primate species, red leaf monkeys , square planter pots and white-bearded gibbons in Gunung Palung National Park, Indonesia using plant phenology data and primate feeding observations collected over 66 months. We examine the feeding ecology of sympatric populations of gibbons and leaf monkeys to: 1) characterize and compare gibbon and leaf monkey diets, identify the genera consumed and their importance, the relative contribution of different plant parts to overall diets, and overall dietary richness, diversity and overlap; 2) analyze feeding selectivity for each primate species; and 3) assess how these primates respond to temporal variation in fruit availability. Specifically, we make the following predictions: compared to gibbons, leaf monkeys will have higher dietary richness and diversity; prefer more genera, and avoid fewer genera; and show shifts in types of plant parts consumed in response to variation in overall fruit availability. We make these predictions based on evidence that leaf monkeys have morphological and physiological adaptations to process a wider variety of foods than gibbons.We conducted this study at the Cabang Panti Research Station in Gunung Palung National Park, West Kalimantan, Indonesia from September 2007 through February 2013. At CPRS, mean gibbon group sizes are 4.32 individuals and mean home range size is 43 ha ; mean leaf monkey group sizes are 5.77 individuals and with 90 ha mean home range size.
There are seven floristically distinct forest types at Gunung Palung National Park, but for the present analyses we focused on the five forest types that exhibit mast fruiting as the non-masting forest types have dramatically different phenological patterns and plant species composition. We operationally define mast fruiting events as periods where there was at least a three-fold increase in fruiting stems above the mean proportion of stems fruiting in all other months. We recorded daily maximum and minimum temperature and rainfall at the field station at CPRS .Each month, AJM, field managers, or trained Indonesian field assistants walked two replicate census routes in each of the seven forest types found at CPRS and collected data on gibbon and leaf monkey feeding behavior. Inter-observer reliability was ensured through extensive training, periodic checks of distance measures, and regular quizzes to assess the accuracy of plant and vertebrate species identifications. Observers were randomly rotated across habitat types and census routes, and average encounter rates and detection distances are highly concordant between observers. Standard line-transect methods allowed for the collection of statistically independent feeding observations and avoided the potential for pseudo-replication that may occur when multiple feeding observations are collected from the same group on the same day. We systematically walked fourteen, spatially segregated line transects, at a consistent speed between 0530 and 1200 hrs . For any group or individual encountered while feeding, we recorded the first item consumed by the first individual seen. We collected feeding data on all age and sex classes, thus adults and juveniles of both sexes were included in our analyses. Because data were collected across multiple forest types and many groups, the results reflect the diet for the population, rather than potentially idiosyncratic observations of a single group. Following collection of feeding data, observations along the vertebrate census route continued so that multiple feeding observations were not made from the same group on the same day. We collected additional feeding data during targeted focal observations of gibbons and leaf monkeys. We selected target groups at random from among the known groups at the site . After contacting the target primate group , we randomly selected a focal individual of any age-sex class and followed until it began feeding. Data collection on focal follows continued for 30 minutes, at which point a new focal individual was randomly chosen. We did not record a new feeding observation from the focal animal until it had travelled to a different tree or liana to ensure that multiple feeding observations were not recorded from the same individual plant. We collected the following data for each primate group encountered on transect routes and during focal follows. For the plant fed upon by the first primate individual sighted, we recorded the identification of the plant eaten , location , size , and growth form of the plant; the part being eaten ; the maturity stage, if applicable ; the number of animals feeding; and an estimate of the total crop size. We gathered one feeding observation every 3.6 days, on average . In previous analyses, we found there were no significant differences in the use of plant genera collected during line transect surveys or focal follows, therefore we lumped feeding observations together to increase sample size.To assess spatial and temporal variation in food availability, we monitored the reproductive behavior of tree and liana stems located in fifty 0.1 or 0.2 ha botanical plots . Each month all stems in every plot were carefully examined with binoculars and assigned to one of six reproductive states . Determination of fruit ripeness stages was based on changes in size, color, and texture, using categories developed over the last 30 years for each plant taxon. Mature fruits are full-sized fruits that are unripe but have seeds that are fully developed and hardened; ripe fruits are the final development stage prior to fruit fall, usually signaled by a change in color or softness.