Together they establish water use objectives and reporting standards for indoor and outdoor residential and commercial use; require SWRCB and CDWR to adopt long-term standards for efficient water use; update urban water management plans to include the reliability of the water supplies and strategies for meeting current and future water needs; require urban water suppliers to conduct a water supply and demand assessment and make water shortage contingency plans available to customers; and require water suppliers to declare emergency measures to ensure sufficient water for human consumption, sanitation and fire protection. AB 2371 was enacted on Sept. 28, 2018. It continues to enforce many current landscape water conservation practices in and out of drought, including hydrozoning, water budgeting, storm water collection, use of recycled water and irrigation equipment maintenance. In addition, it requires the Contractors State License Board to update the C-27 landscape contractors’ exam as needed to include questions on new and emerging landscape irrigation efficiency practices; allows potential purchasers of housing units containing in-ground landscape irrigation systems to require irrigation system inspections; and requires the formation of a working group to examine and consider updating current consumer information on landscape water use. It also requires CDWR, following a public hearing every 3 years,hydroponic nft channel to update MWELO or determine that an update is not needed and consider revising and updating the WUCOLS database.

UC continues to play a major role in providing objective information to policymakers as they formulate and update legislation on water conservation in commercial and residential landscapes. UC also continues to advance the science to conserve water and help ensure that legislative targets are met. Due to continued improvements in the efficiency of sprinkler and drip irrigation systems , ETAF was further reduced in 2015 from 0.7 to 0.55 for residential landscapes and from 0.7 to 0.45 for commercial landscapes . Conservation on this scale will rely heavily on implementing best practices that decrease water loss, identifying new species of drought-resistant landscape plants and improving irrigation system performance. In practice, many irrigation systems fall far short of the irrigation efficiencies used in the current MWELO. Bijoor et al. found that smart irrigation systems were more effective at reducing water loss than irrigation systems operated by conventional timers and that the difference exceeded water savings realized from selecting a warm-season turf species over a cool-season species. Reid and Oki continue to screen a wide variety of landscape plants for their drought resistance to expand the palette of California-friendly landscape plants. Work by their team has already led to the identification of hundreds of drought-resistant plants included in MWELO. UC ANR Specialist Amir Haghverdi is leading a project to further define water requirements of turf under deficit irrigation and reclaimed water regimes; evaluate the performance of soil moisture–sensing and ET-based smart landscape irrigation technologies on water use effectiveness under deficit irrigation; and monitor turf responses to multiple levels of water stress using multi-spectral and thermal remote-sensing techniques.

David Fujino and the Western Center for Agricultural Equipment established the Smart Landscape project at UC Davis in collaboration with more than 20 organizations and companies. Smart Landscape provides workshops and on-site training for landscapers and students on new water-saving technologies. Several UC faculty, specialists and advisors are involved in various projects throughout the state alone and in cooperation with the U.S. Forest Service and other groups to determine the long-term durability of a wide variety of underused landscape trees under warmer, drier conditions due to climate change and urban heat islands.Horticulture likely originated 20,000years ago. There are over 100 species of horticultural crops, consisting of diverse fruits, vegetables, and tubers, many of which are of high economic value with enormous production volume worldwide. The amounts of fruits, vegetables, and tubers produced in 2018 were 868, 1089, and 832 million tons respectively , and the increased demand from a growing, and afuent global population, is predicted to drive further expansion of horticultural output. Horticultural crops not only provide basic calories , but also, are among the most crucial sources of fiber, organic acids, micro- and macro minerals, vitamins, and antioxidants in human diets. Healthy attributes, and a wide range of tastes, textures, and favors make horticultural crops attractive. Starch is critical to human society given its versatile uses. Starch is the dominant energy source in the human diet, providing over 50% of our daily caloric needs. In the food industry, starch is widely used as a thickener, stabilizer, lipid replacer, defoaming agent, gelling agent, emulsifer, and dietary fiber, and in the pharmaceutical industry, starch is used as an excipient for drug delivery . In addition to these diverse uses, starch is an excellent renewable material for making ethanol biofuels and degradable ‘bioplastic’ products. Starch is almost ubiquitous in higher plants, including horticultural crops, in ways that may or may not be noticed.

For instance, potato, sweet potato, yam, and cassava are starchy, but spinach, lettuce, and ripe tomatoes, berries, and citrus are not, yet starch is likely to be important to the growth, development and fitness of all of these crops, as they are in better studied models. The widely accepted view is that starch accumulates either in a transitory state, or for long-term storage starch. Transitory starch follows a diurnal pattern: it is synthesized and accumulated directly from the products of photosynthesis in the leaf and in the stem during the daytime, and is then degraded into sugars as an energy source for the following night. In comparison, storage starch is defined as that located in perennating organs such as seeds, grain, embryos and tubers , where it provides sustenance for the next generation during germination and sprouting in sexual and asexual propagated crops, respectively. A third class of starch: ‘transitory-storage starch’ has been proposed. It describes starch that is accumulated and degraded during development in the storage organ. Transitory-storage starch is a feature of many species including horticultural crops of economic value such as tomato, banana, kiwi, strawberry, nectarine, and apple fruit . Starch accumulates as semi-crystalline, water insoluble granules that vary in diameter from 1 to 100μm depending on species. Starch is organized into two glucan polymers: amylose and amylopectin. Amylose and amylopectin consist primarily of linear chains of glucoses joined by α-1,4-glycosidic bonds. In amylopectin,vertical farming racks the α-1,4-glucan chains are branched more frequently through α-1,6-glycosidic bonds, compared to amylose. The branching of the amylopectin chains is such that chains of diferent lengths are produced: short, medium and long chains, and the frequency with which each fraction occurs influences starch functionality. Side chains of amylopectin form clusters around branching points, and two adjacent chains make up a double helix. These physical features of amylopectin polymers leads to a semi-crystalline granule; amylose with a randomly coiled conformation, fills the matrices within the granule. Amylopectin and amylose account for around 25 and 75% of the starch in major heterotrophic storage organs, respectively, while the starch in leaf tissues is approximately 5 – 10% amylose.Amylose and amylopectin are synthesized by the coordinate action of a group of four key enzymes. The core starch biosynthetic enzymes include ADP-glucose pyrophosphorylases , starch synthases , starch branching enzymes , and de-branching enzymes , of which there are many isoforms. In brief, AGPases initiate the frst step of starch biosynthesis by catalyzing the formation of ADP-glucose. SSs elongate the glucan chains in amylose and amylopectin; SBEs branch the glucan chains, while the DBEs shorten and modify the starch chains which enable a higher-order semicrystalline structure to form. SBEs, the focus of this review, hydrolyze α-1,4-linked glucan chains, and attach the newly-created ‘free’ chain to another glucan chain within the starch granule, via an α-1,6-linkage. Through this action, SBEs largely determine the proportion of the relatively unbranched amylose to the highly-branched amylopectin. Two major classes of SBEs are bio-functionally known: SBE1 and SBE2 , and they vary in terms of their substrate selectivity, whereas the function of SBE3 awaits verifcation across a broader set of species. SBE1 preferentially branches ‘amylose-like’ long glucan chains as the substrate, while SBE2 prefers a more branched substrate.SBEs are the key players in the regulation of the amylose-to-amylopectin proportion in plants. However, their functions in many harvested horticultural crops have been under-investigated, although evidence points to the importance of starch in determining the post harvest quality of these crops.

We aimed to develop a better understanding of the role of SBEs in fruits, tubers, and leafy greens in physiological processes by exploring SBE sequence relationships, expression, and starch phenotypes in diverse crops.SBEs have three classes of isozymes including two functional SBE classes and one putative class 3 SBE . SBE1 isoforms appeared earlier than SBE2 and SBE3 in the viridiplantae, but plant SBE1 and SBE2 are more homologous to each other, than to SBE3. SBEs have been identified and relatively well-characterized in cereal crops, tubers, and Arabidopsis thaliana over the last two decades ,but, as mentioned, little attention has been paid to the diverse group of species that are classified as horticultural crops. Within each class of SBE, the cereals grouped together, while most non-cereals formed another cluster . This pattern is due to the divergence of monocots from dicots around 200 million years ago. In contrast to the presence of ‘a’ and ‘b’ sub-isoforms of SBE2 in cereal crops, horticultural plant species generally have one SBE2 isoform. It was also observed that not all species have a known or predicted class 3 isoform. The SBE sequences contained within diverse organs, i.e., fruits, tubers, roots, and leafy vegetables , clusThered together based on their respective plant families. Te class 1 SBE is absent in Arabidopsis thaliana, and so it was not surprising that this SBE class is not present in the Brassicaceae. However, the class 1 SBE is also absent in apple , and European olive , but these species all have two class 2 SBE isoforms . In addition, banana contains at least four types of SBE2, and transcripts corresponding to these SBE2s have been identifed, indicating that they are expressed.Starch Branching Enzymes belong to the α-amylase family of enzymes, specifically the glycoside hydrolase family 13 super family, with multiple isoforms encoded by diferent genes . The overall structure of the SBE polypeptide is highly conserved: all SBEs possess a central α-amylase catalytic domain , and an NH2- terminus, and a carboxyl- terminus. The SBE NH2-terminus contains two conserved domains: a chloroplast transit peptide for plastid-targeting, and a CBM48 domain for binding to starch. The C-terminus contains the residues that determine substrate preference and catalytic activity. The central region of the enzyme contains the “A” catalytic domain, that is made up of 8–barrels. Notably, the class 3 SBE may not directly participate in starch biosynthesis in Arabidopsis, but it has a demonstrated function in mediating cesium toxicity of photosynthesis. However, the role of SBE3 is unlikely to be conserved. In potato, StSBE3 has a unique coiled-coil motif which is absent in the AtSBE3 polypeptide . Notably, the CBM48 domain is also deficient in AtSBE3 . It is possible that the StSBE3 may interact and complex with other starch biosynthetic enzymes through its coiled-coil domain, in a similar way to the SS4-PTST2 interaction in Arabidopsis, the GBSS-PTST1 interaction in rice or the SBE containing protein complexes in cereal endosperm , rendering an assistant function in starch biosynthesis. This species-specific mode of action of SBE3 may reveal a novel function of SBEs generally. Indeed, although all SBEs are predicted to form complexes with starch phosphorylases , the starch synthases and isoamylase , interactions with other proteins show differences depending on the species and SBE isoform.Four conserved regions critical for catalysis, named Regions 1-4 , are found within the catalytic A-domain . Regions 1-3 are directly involved in catalysis, while Region 4 is involved in direct substrate binding. SBE1 and 2 have largely invariant residues, but the residues in the SBE3 isoform of many species have substitutions at these sites. Post-transcriptional phosphorylation of the SBE-protein complexes formed with other starch biosynthetic enzymes has been found in cereal crops and in cassava, while experimental evidence of this regulation in the majority of horticultural crops is absent. SBE1 and SBE3 have fewer possible phosphorylation amino acid sites than SBE2 .